A Catholic-led fight to overturn contraceptive mandates in the health care law has drawn big dollars, large crowds and prominent GOP backing, raising questions about how aggressively Catholic bishops might wade into politics.

A two-week “Fortnight for Freedom” campaign organized by the U.S. Conference of Catholic Bishops culminated July Fourth with a rally-style celebration that was expected to draw some 4,000 people to the Basilica of the National Shrine of the Immaculate Conception in Washington, D.C.

The two-week campaign, organized on the ground by the Catholic Association, a group of lay Catholics, also featured TV and Web advertising, petitions aimed at Members of Congress and email and text messages to a million Catholics.

Joining in the effort were Conscience Cause, a group launched in April by two prominent Republicans that includes Catholics and non-Catholics, and Catholic Vote, a nonprofit and super PAC that backs presumed GOP presidential nominee Mitt Romney and aims to spend $5 million or more in this election.

The Catholic bishops have also helped to organize a dozen lawsuits lodged by archdioceses around the country challenging the law’s mandate that health care plans include contraceptive services. Responding to critics, the Obama administration shifted the cost of coverage to insurers and wrote an exception for religious organizations.

But critics say the administration’s definition of a religious organization is too narrow and would force many religious schools, employers and charities to provide services that violate their religious beliefs. All told, 56 plaintiffs have filed 23 lawsuits challenging the Health and Human Services Department mandate, including three Protestant educational institutions.

“We have seen an incredible intensity on this issue,” said Maureen Ferguson, a senior policy adviser at the Catholic Association, which was founded in 2007 but relaunched itself this spring to focus on the contraceptive mandate.

Another new player is Conscience Cause, which promotes religious freedom for all denominations, potentially galvanizing non-Catholics on the issue. The group has gathered 6,000 signatures on a petition aimed at forcing a vote in Congress to rescind the reproductive health mandate.

“We believe that this is the viable option because this is nonpartisan,” said Conscience Cause Executive Director Christen Varley, a former tea party organizer. “It’s a faith issue. It’s a constitutional issue.”

But some argue the campaign is overtly political. Conscience Cause is the brainchild of two prominent Republicans now advising the Romney campaign: former Republican National Committee chairman and Veterans Administration Secretary Jim Nicholson, a major GOP fundraiser who is helping Romney reach veterans and Catholic voters; and Ed Gillespie, another former RNC chairman who sits on the group’s board and is a senior Romney strategist.

Republicans are drawn to the fight over mandates both because they could galvanize Catholics, a key swing voting bloc, and because the issue could resonate with influential Evangelical voters. At one “Fortnight for Freedom” rally last month, Catholic bishops in Kansas fired up a large crowd alongside GOP Gov. Sam Brownback.

“One of the few options now available to repeal the flaw [in the law] is going to be the ballot box,” said Brian Burch, president of Catholic Vote. A Catholic Vote Web video featuring stirring music and patriotic scenes casts the mandate as a violation of civil and religious rights and warns: “Mr. President, You’ve Awakened a Sleeping Giant.”

Burch said Catholic Vote will be active in the presidential and Senate elections and use sophisticated, new microtargeting tools to reach Catholics with Internet ads. Conscience Cause also is doing Internet advertising, Varley said, and is considering voter guides and rallies in key Congressional districts.

The highly politicized campaign has drawn fire from progressive Catholics, watchdog groups and even some bishops. Stockton, Calif., Bishop Stephen E. Blaire told a Catholic newspaper in May that “different groups … are trying to co-opt this and make it into a political issue.”

John Gehring, Catholic program director at the progressive group Faith in Public Life, drew a lengthy rebuttal from the U.S. Conference of Catholic Bishops when he challenged the campaign in a memo to reporters.

“It’s kind of a stretch to make the case that this is simply an educational effort, when some bishops seem happy to align with Republican politicians in a national mobilizing campaign against President Obama just a few months before a national election in which Catholics will play a decisive role,” Gehring said in an interview.

In a statement released to the media last month, Barry Lynn, executive director of Americans United for Separation of Church and State, pointed to tax rules that bar charities from partisan politics: “The bishops have been far from even-handed in their political activities. At some point, it may raise questions about compliance with federal tax law, which forbids [charitable] tax-exempt organizations from favoring or opposing candidates for public office.”

The bishops counter that their “Fortnight for Freedom” is about prayer, not politics.

“It’s important to say the struggle we are engaging in here is not a partisan issue,” Baltimore Archbishop William Lori said last month in a conference call with the Catholic Press Association. “We didn’t choose the time. We didn’t choose the place.”