A Planned Parenthood office in Peoria, Ill., on Dec. 16, 2016. (Daniel Acker/Bloomberg News)

Planned Parenthood on Thursday launched a campaign to resist congressional efforts to target the organization, with marches, letter-writing campaigns and other activities planned in dozens of cities over the next three months to demand that lawmakers abandon efforts to undermine a source of health care for 2.5 million Americans.

The campaign coincides with the start of the new Congress, whose Republican leaders have pledged to end federal funding to the 100-year-old group, which receives about $500 million in federal grants and Medicaid reimbursements and is known for providing reproductive health care to women, including abortions. President-elect Donald Trump, who takes office later this month, has said he would sign such a bill.

As part of the new campaign, Planned Parenthood aims to show the deep support it has from men and women across the country, including from some who voted for Trump. They are linking their struggle to broader concerns about women’s issues, prompted in part by Republicans’ plan to repeal the Affordable Care Act, which allowed 55 million women to receive birth control through their health insurance without a co-pay. They also plan to highlight the records of several of Trump’s Cabinet selections and his vice president-elect, who oppose abortion rights and government efforts to widen access to birth control.

If these appointees “had their way, millions of people across the country would be stripped of their access to basic health care,” Kelley Robinson, deputy national organizing director for Planned Parenthood, said in a statement. “We won’t back down, we won’t be silenced, and we will not let these politicians attack our health and rights without a fight.”

After Donald Trump's many shifting comments about women's health and reproductive rights, some women are worried about what will happen under the new administration. (Jenny Starrs/The Washington Post)

Conservatives have longed to cut off federal funding to Planned Parenthood because of its role as an abortion provider and its advocacy on abortion rights. Abortion foes see an unprecedented chance to fulfill that hope now, with Republicans in control of Congress and the White House for the first time in a decade.

But Planned Parenthood supporters plan to push back aggressively. They cite the organization’s resilience in the face of repeated attacks over its history, as well as widespread support for what it considers the bulk of its work — birth-control prescriptions, cancer screenings, tests for sexually transmitted diseases and other non-abortion-related health care provided through dozens of affiliate health centers across the country. In a January 2016  CBS News-New York Times poll, 57 percent of those surveyed said Planned Parenthood should continue to receive funding from the federal government.

Trump campaigned on economic concerns over social issues, raising questions about his willingness to engage in fights over issues such as abortion. And while he has said he supports repealing the health law and cutting funds to Planned Parenthood, he has made approving comments about aspects of the law as well as Planned Parenthood ‘s non-abortion work.

Moreover, a tumultuous day in Congress on Wednesday exposed the depths of divisions within the Republican Party, suggesting that there are limits to the ability of conservatives to achieve their agenda.

Still, conservative lawmakers telegraphed their plan to continue to press their case against Planned Parenthood with a fresh report, issued this week, calling for the organization to lose its federal funding over a controversial fetal tissue donation program, alleging that “Planned Parenthood affiliates and clinics have repeatedly neglected their fiduciary duty requiring good stewardship of federal taxpayer dollars.” Planned Parenthood officials criticized the report as a partisan attack.