Democratic lawmakers, fearful that President Obama is on the verge of significantly diluting a proposed regulation that would give millions of women access to birth control without out-of-pocket insurance charges, are furiously lobbying the White House to hold the line.

At issue is whether the provision, announced in August, should exempt a far broader range of religious organizations than originally proposed.

In a phone call with senior White House adviser David Plouffe on Tuesday afternoon, eight senators argued that the consequences of expanding the exemption would be devastating, according to people familiar with the call.

Sen. Jeanne Shaheen (D-N.H.) also raised the issue with Obama while she was with him in New Hampshire on Tuesday, her spokesperson said. These talks followed conference calls last week between other top White House officials and members of the Congressional Pro-Choice Caucus.

“I think in the 21st century, most people are stunned to hear that we would even be talking about whether women can buy birth control through their insurance policies,” said Rep. Diana DeGette (D-Colo.), a leader of the group, who participated in one of last week’s calls. “You would be denying millions of Americans the ability to have an essential part of their insurance coverage because of some attenuated religious affiliation of their employer.”

The contraceptive-coverage rule — proposed by Health and Human Services Secretary Kathleen Sebelius in August — expands on a more general provision in the 2010 health-care law that requires all new insurance plans to cover preventive services specified by Sebelius without co-pays, deductibles or other out-of-pocket costs. In including birth control, Sebelius suggested exempting nonprofit groups whose purpose is to inculcate religious values and that primarily employ and serve people who share those values.

That definition prompted an outcry from representatives of religious groups, including the U.S. Conference of Catholic Bishops. They argued that the exception was so narrow that virtually the only qualifying organizations would be churches. Left out would be a host of religion-affiliated institutions such as Catholic hospitals, schools and clinics.

“You are forcing a Catholic organization to pay for something that goes directly against its belief system,” said Sister Mary Ann Walsh, a spokeswoman for the bishops.

She said it is also unfair and illogical to treat Catholic social service agencies as the equivalent of secular ones simply because they serve many non-Catholics. Their Christian faith is what drives such groups to serve needy people regardless of religion, she said. “We serve people because we’re Catholic, not because they’re Catholic.”

At a news conference in August announcing the proposed rule, Sebelius said that because birth control is the most common drug prescribed to women ages 18 to 44, not including it “would be like not covering flu shots.”

So as the bishops conference and other religious groups campaigned for a broader exemption, Planned Parenthood President Cecile Richards said it seemed “unthinkable” that the administration would incorporate those suggestions in the final rule — which will take effect beginning Aug. 1, as insurance plans renew.

Then, two weeks ago, Obama met with Archbishop Timothy M. Dolan of New York, the president of the U.S. Conference of Catholic Bishops. The bishops’ relationship with Obama has been difficult, with disagreements about the contraceptive-coverage mandate and other issues.

But Dolan’s upbeat comments after the meeting suggested that a compromise on the birth-control mandate could be in the works. When administration officials declined to tamp down the rumors, the policy’s advocates in Congress — including some of the president’s staunchest allies — pronounced themselves shocked.

“What’s baffling is not just the policy, but the political calculus here,” said Sen. Richard Blumenthal (D-Conn.). “The effect would be to undermine, if not eviscerate, the energy and enthusiasm of huge numbers of young people, women and independent voters who believe in the president.”

It is unclear what new language the administration may be considering. One possibility is that any religiously affiliated nonprofit could be exempt from the coverage mandate. Given the hundreds of thousands employed by Catholic hospitals, universities and schools alone, the number of people who could be affected could be significant.

A portion of those who work or study at religious institutions already are covered by plans that include birth control, often because the plans are licensed in one of 28 states that have contraception-coverage mandates.

However, if their organizations were to be exempted from the federal rule, these individuals would have to continue paying out-of-pocket charges for birth control — about $20 to $30 per month, according to Planned Parenthood.

Taina Vargas would not even have that option. Vargas, a graduate student studying for a master’s degree in diplomacy and international relations at Seton Hall University, said she was surprised to learn that the Catholic institution's health plan does not cover her birth-control prescription.

“This really is an issue of principle for me,” said Vargas, who is not Catholic. “If young women like myself choose to be sexually active and don’t want a child right now so we can focus on our education, I think [birth control] is something the university should provide. . . . I don’t think it’s right for someone else to make this decision for me.”

Walsh countered that complaining that a Catholic organization doesn’t cover birth control is like complaining that it displays crucifixes. “When people work for a Catholic institution, they should expect a Catholic identity.”