Activists demonstrate in front of the Supreme Court in Washington on June 27, 2016. (J. Scott Applewhite/AP)

Planned Parenthood officials are scrambling to prepare for the likelihood that Congress next year will cut off more than a half-billion dollars in federal funding to the group, fulfilling the wishes of abortion foes who are planning an aggressive push to roll back abortion rights under President-elect Donald Trump.

Officials with the 100-year-old women’s health nonprofit organization are leaning on donors, new and old, and preparing to lobby friendly lawmakers at the state and local level to stem some of the loss. They have started gaming out which communities might be able to withstand a loss of services. They are asking supporters to get their medical care at Planned Parenthood clinics to increase the proportion of privately insured patients.

The effort to defund Planned Parenthood is likely to be just the opening salvo in a new battle over abortion rights touched off by the election. Empowered by joint Republican control of Congress and the White House for the first time since 2006, antiabortion activists see a historic opportunity to outlaw certain procedures and perhaps reverse Roe v. Wade, the Supreme Court decision that legalized abortion nationally four decades ago.

Rep. Diane Black (R-Tenn.) said in an interview that she plans to introduce a bill that would eliminate the provider’s funding as “one of the first orders on the agenda” when the new Congress convenes next month.

The federal dollars to Planned Parenthood — most of which flow to the organization in the form of Medicaid reimbursements — make up more than 40 percent of its budget. Such a loss, Planned Parenthood officials say, would force them to close many programs and turn away many of the 2.5 million patients their clinics see annually.

Planned Parenthood activists express their concern about President George W. Bush's nominee for the Supreme Court, John G. Roberts Jr., in front of the Supreme Court July 20, 2005, in Washington. (Joe Raedle/Getty Images)

“Obviously we are doing everything we can through advocacy and everything else to make sure we can continue to serve patients,” said Erica Sackin, spokeswoman for Planned Parenthood. “But at the end of the day, this is a fight of a scale that we haven’t seen before and we need to be realistic about how much is at stake.”

Among the other hopes of antiabortion groups that now seem plausible: A federal ban on dilation and extraction, the most common abortion procedure in the second trimester. Legislation to make permanent the Hyde Amendment, currently renewed every year, to bar federal funds from being used to pay for abortions. A ban on the procedure at 20 weeks of pregnancy.

And with Trump’s pledge to appoint justices who oppose Roe v. Wade , the 1973 Supreme Court decision legalizing abortion nationwide, abortion foes also see a chance to overturn that landmark ruling. Last week, in a direct challenge, Ohio lawmakers passed a ban on abortions as soon as a fetal heartbeat can be detected, as early as six weeks. Gov. John Kasich (R) has not yet said if he will sign the measure.

The first strike, however, is likely to be aimed at crippling an organization that not only performs more than 300,000 abortions a year but also is the best known advocate for the unfettered rights of women to obtain the procedure.

Planned Parenthood’s federal funding comes primarily from Medicaid as well as Title X, which provides family-planning grants. Although the money cannot be used for abortions, critics say it indirectly supports the procedures and that Americans want no part of such work.

“It is time that taxpayers are taken off the hook for supporting an organization that supports the killing of innocent children,” said Rep. Trent Franks (R-Ariz.), a longtime Planned Parenthood foe.

Antiabortion groups have urged congressional leaders to try to defund the group immediately in the new Congress as part of the budget reconciliation process, which requires a simple majority to pass. They sent a similar bill to President Obama in 2015; he vetoed it. Trump has pledged to sign such a measure.

Ohio lawmakers passed a bill that would prohibit abortion as soon as a fetal heartbeat can be detected — at around six weeks, before many women realize they are pregnant. Here's what you need to know about the bill. (Thomas Johnson/The Washington Post)

“It was one of the conditions that the pro-life movement had” for supporting Trump, said Penny Nance, president of Concerned Women for America, a conservative group. Since his election, Trump has not addressed the controversy over Planned Parenthood and his transition team did not return a request for comment.

Such a vote is likely to meet fierce resistance among reproductive rights advocates, who would no doubt challenge the effort in court. Federal law protects the right of patients on Medicaid to use the providers of their choice, and previous efforts at the state level to defund Planned Parenthood have been blocked by the courts.

But Congress has broad leeway in setting laws, and it is likely that the decision would ultimately rest with the Supreme Court.

“We know that we have the will in both the House and the Senate” to pass a new version of the Defund Planned Parenthood Act, said Black, as well as willing partners in Trump and Vice president-elect Mike Pence, who as governor of Indiana signed one of the nation’s strictest abortion laws. While in Congress, Pence filed the first legislation to bar Planned Parenthood from receiving federal dollars and tried to shut down the government over giving money to the organization.

There are other ways the Trump administration could target the organization. The Health and Human Services Department could back off what has been an aggressive defense under the Obama administration to stop states from cutting off Medicaid funds to the group. The Justice Department could redouble efforts by Congress to find evidence, so far lacking despite multiple investigations, that Planned Parenthood illegally sold fetal tissue for a profit.

In several polls over the past year, sizable majorities of respondents opposed cutting off all funding to Planned Parenthood. In a January CBS News/New York Times poll, 57 percent of those surveyed said Planned Parenthood should continue to receive funding from the federal government.

Across the country, leaders of Planned Parenthood’s 52 affiliates are groping their way forward, unsure of exactly what is to come but operating with certainty that it will be bad. They spent part of last week in Washington, exchanging notes and strategizing.

The impact is likely to be greater for clinics that have a large number of patients on Medicaid, and less so on clinics that have fewer Medicaid patients. States that have more restrictive Medicaid policies have taken away the state matching portion of Title X funding. Other states, including Kansas, have refused to disburse Title X dollars to Planned Parenthood.

Nationally, about half of the organization’s patients rely on Medicaid to get their preventive care, raising the prospect that a complete loss of federal funds will force clinics to turn some patients away.

Laura McQuade, president and chief executive of Planned Parenthood Great Plains, which serves four states, believes her health centers will be in a better position than others: Republican governors and legislators have already stripped away much of the federal funding her organization receives. She is asking donors who have private insurance to start using Planned Parenthood as a health-care provider to boost revenue.

“Blue-state affiliates, for lack of a better phrase, are going to be hit much, much harder than those of us operating in deeply red states. We have lost the majority of our money already,” she said.

Vicki Cowart, president of Planned Parenthood of the Rocky Mountains, which covers all or parts of five states, said her staff is analyzing which clinics might be most affected. A program that provides vasectomies to men in New Mexico, for instance, would have to shut down if its funding source, Title X, is cut off.

“We’re looking at this from a massive planning perspective, but then you put yourself in the shoes of the person who needs a vasectomy, and it’s a profound event for them,” she said. “The cost of human misery in this setting is huge, and I don’t want us to lose sight of the fact that these are people, not some stupid political game.”

Communities that have been supportive of Planned Parenthood are pledging to step in if the organization is defunded. New York Mayor Bill de Blasio (D) last week tweeted that “if GOP threatens federal funding for Planned Parenthood of NYC, we will ensure women receive the health care they need.”

Anxious women have flocked to Planned Parenthood out of fear that their nearby clinic will close or policy changes might make birth control or other health care harder to get. In the immediate aftermath of the election, the organization said, there was a 10-fold increase at its clinics in the number of women seeking intrauterine devices — a long-acting and costly form of birth control that is now available for many women free of charge because of the Affordable Care Act.

The organization also said it has seen a surge of donations, some offered in Pence’s name as a jab at the incoming vice president, and a flood of people seeking to volunteer.

Amid all the uncertainty, clinics have sought to reassure patients that they have withstood political attacks before and will do so again.

“Planned Parenthood is not about to go away based on anything that happened in this election,” said Sarah Stoesz, president of Planned Parenthood of Minnesota, North Dakota and South Dakota. “We’ve built muscle over 100 years.”

Scott Clement contributed to this report.