The U.S. Conference of Catholic Bishops plans to work with other religious groups, including evangelical Christians, on an election-year public relations campaign that may include TV and radio ads, social media marketing and a push for pastors and priests to raise the subject from the pulpit.

"We want to make it something that will get peoples' attention," said Bishop William Lori of Bridgeport, Conn.

The bishops spent the past few weeks pressing President Barack Obama to exempt religious employers from a federal mandate that all health insurance plans offer free birth control.

Obama agreed to modify the mandate a bit, so that religious employers wouldn't have to pay for contraceptive coverage directly. That satisfied some Catholic groups, but the bishops were not mollified. They want the mandate repealed altogether.

And now, they are aiming higher still, lobbying Congress to enact a law that would let any employer opt out of covering any medical treatment he disagreed with as a matter of his personal faith.

So, for instance, a pizzeria owner who objected to childhood vaccinations on religious grounds would be able to request an insurance plan that did not cover them, in effect overriding a federal requirement that vaccinations be provided free with any health-insurance plan.

Leaving coverage decisions up to each employers' conscience might create chaos in the marketplace, "but chaos is sometimes the price you pay for freedom," said Richard Land, the president of the Southern Baptist Convention's Ethics & Religious Liberty Commission, who is backing the bishops whole-heartedly.

Democrats, who control the Senate, are likely to block any bill with such broad opt-out provisions.

But supporters, including prominent Republicans, say they will keep pushing for the change, which fits into a wider theme of defending individual freedoms against government intrusion which is expected to play prominently in the November election.

MESSAGE FROM THE PULPIT

Along with the Southern Baptist Convention, the National Association of Evangelicals stands ready to contribute money and manpower to the bishops' campaign, said Galen Carey, an association vice president.

The group is also considering the unprecedented step of asking pastors of every evangelical denomination across the country to read their congregations an open letter protesting the contraception mandate as an assault on religious liberty.

Liberal groups are already launching counter-attacks.

This week, NARAL Pro-Choice America, which works to keep abortion legal and expand contraceptive access, spent $250,000 to air radio ads in four swing states that will be crucial to the presidential election -- Colorado, Florida, Virginia and Wisconsin.

The ads urge support for Obama and his effort to ensure that "women of all faiths, no matter where they work," can get free birth control with their health insurance.

More than 30 organizations supporting Obama teamed up to create the Coalition to Protect Women's Health Care, which has started an online petition and plans further action.

The coalition includes two unions that represent millions of workers and have well-honed networks for getting out political messages, the Service Employees International Union and the American Federation of State, County and Municipal Employees.

Obama's supporters say the president went far enough to accommodate religious institutions when he announced last week that they wouldn't have to pay for free birth control as part of their insurance plans; he said instead their insurers would be required to pick up the costs.

The bishops denounced this as a gimmick that doesn't solve anything, especially for the many religious hospitals and schools that self-insure their employees.

"Reasonable people should be able to work through the details of this and find common ground," said John Gehring, Catholic outreach coordinator for the liberal group Faith in Public Life. "But election-year politics doesn't make for cool heads."

BATTLE FOR RELIGIOUS FREEDOM

The Conference of Catholic Bishops began preparing months ago for a battle royale over religious freedom. Last fall, the conference bulked up its staff, hiring a lawyer who had devoted his career to religious liberty cases and a lobbyist to press the cause in Washington. The group also created a special committee on religious liberty, chaired by Bishop Lori.

In a September letter announcing the committee, Archbishop Timothy Dolan declared that religious freedom "is now increasingly and in unprecedented ways under assault in America." He and other officials offer many examples of that perceived assault.

On the federal level, the Obama administration has cancelled or threatened to cancel contracts awarded to Catholic charities for work to prevent HIV and to help victims of sex trafficking. The administration says the charities have to provide services such as condoms, emergency contraception and abortion referrals to maintain the contracts; the charities protest that such conditions violate their religious faith.

Several states, meanwhile, have required adoption agencies that receive public funds to treat same-sex couples on par with any other prospective foster or adoptive parent. Catholic Charities object, saying the church doesn't sanction gay and lesbian relationships. Rather than comply with the laws, bishops in Illinois, Massachusetts and Washington D.C. have shut down Catholic adoption agencies.

The bishops portray this as an out-and-out war on free exercise of religion.

But secular and liberal groups say no one's assailing the freedom to worship, to proselytize -- or even to perform social services, such as placing needy children in loving homes, according to religious precepts.

It is only when a religious institution accepts taxpayer money to do such work that religious freedom must take a back seat to secular laws, said Marci Hamilton, a constitutional scholar at Cardozo School of Law.

Courts nationwide have repeatedly ruled that religious groups must follow the same rules as everyone else when holding a government contract, Hamilton said. Any institution that can't in good faith follow those rules shouldn't apply for public funding, she said.

GUARDING CONTRACEPTION

With regard to contraceptive care, courts in New York and California have upheld state laws -- similar to the federal mandate -- that insurance plans, including those sponsored by religious employers, must cover birth control if they cover other prescription drugs.

It is unclear whether such nuances will filter into the public debate over religious freedom and contraceptive coverage.

Both sides say they believe public opinion is firmly in their corner -- and they're determined to keep it that way with a steady drumbeat of snappy soundbites.

More than 100 university professors and religious leaders from different faiths released a letter of protest against the administration Tuesday that was headlined with a single word: "Unacceptable." The letter called the Obama administration "morally obtuse" and blasted the contraceptive coverage mandate as "a grave violation of religious freedom."

On the other side, the American Civil Liberties Union held a press conference to accuse the bishops of playing politics in the name of faith. The bishops are promoting "a distorted view of religious liberty -- one that has no basis in law or the Constitution," said Daniel Mach, director of the ACLU Program on Freedom of Religion and Belief.

(Reporting By Stephanie Simon in Denver,; additional reporting by Thomas Ferraro; Editing by David Storey and Marilyn Thompson)

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