The Internal Revenue Service has work to do. It has avoided investigating complaints of partisan political activity by churches, which has encouraged religious groups to endorse election candidates – overtly or tacitly – in defiance of their tax-exempt status. The IRS needs to start minding the store.

The violations – or the appearances of them – are bold. According to an Associated Press story, the pastor of an independent church in Texas posted a pre-election sign that read “Vote for the Mormon, not the Muslim.” Republican Mitt Romney is a Mormon and while President Obama is a Christian, many opponents, either out of ignorance or a pathetic attempt to discredit him, insist he is a Muslim.

Just before the election, the Billy Graham Evangelistic Association took out full-page ads in major newspapers, including The Buffalo News, urging Americans to vote along biblical principles. A picture of Graham, who met last month with Romney and pledged to help his cause, was prominently featured in the ad.

Nor is it only Republican clerics who are flouting the law. A recent survey by the Pew Forum on Religion and Public Life found that 40 percent of black Protestants who attend worship services regularly said their clergy have discussed a specific candidate in church – and that candidate was always Obama.

This would be a delicate matter for any administration, but perhaps especially for Obama’s, given the new requirement that church-related businesses, including hospitals and schools, provide free birth control to women in their health insurance plans.

But the IRS rule should be enforced. It doesn’t broadly prohibit political activity by churches, restricting them only from participating or intervening in “any political campaign on behalf of [or in opposition to] any candidate for public office.”

The Supreme Court has approved that regulation, ruling that the issue is not a matter of free speech, but whether the government will subsidize those activities through a tax exemption.

The lack of enforcement traces to a 2009 federal court ruling that required the IRS to clarify which high-ranking official could authorize audits over the tax code’s political rules. The IRS has yet to do so. It should, and it should then get busy.

That doesn’t mean the IRS should be busting down the doors of churches and hauling pastors to the pokey. But it is time to turn up the heat and issue clear warnings that continued violations could cost the churches their tax-exempt status.

Churches serve many vital roles in society, but endorsing political candidates should not be one of them. If we can trust any organizations to follow the rules – rules they agreed to when they secured tax-exempt status – it is the nation’s churches.