A dozen U.S. senators sent a stern warning to the Internal Revenue Service yesterday: Don’t let politics play a role in recent inquiries of Tea Party organizations.

In the past few months, the IRS sent detailed questionnaires to organizations in Kentucky, Ohio, Tennessee and Texas asking about their political activities. Many of those groups have applied for tax-exempt status under Section 501(c)(4) of the tax code.

The IRS inquiry comes amid attacks on Tea Party groups from liberals, including seven Democrats who wrote to the IRS last week. “We urge the IRS to prevent abuse of the tax code by political groups focused on federal election activities,” Sen. Chuck Schumer (D-NY) and his colleagues wrote. (Schumer has a history of attacking Tea Party groups, even shutting down a meeting on Capitol Hill last year.)

Schumer’s letter urges the IRS to limit the amount of political activity by tax-exempt organizations that don’t disclose their donors. Schumer threatened to introduce legislation if the IRS didn’t take steps administratively.

Yesterday, Republicans responded. Sens. Orrin Hatch (R-UT) and Rob Portman (R-OH) signed a letter along with 10 colleagues to IRS Commissioner Douglas H. Shulman. (Full text of the letter is below.)

“It is critical that the public have confidence that federal tax compliance efforts are pursued in a fair, even-handed, and transparent manner — without regard to politics of any kind,” the Republican senators wrote.  “It is imperative that organizations applying for tax-exempt status are able to rely on a consistent and foreseeable review structure from the IRS.  Any significant changes to the IRS review process should be implemented only after appropriate notice and opportunity for comment from the public and affected parties.”

The American Center for Law and Justice is currently representing nearly 20 Tea Party groups facing IRS inquiries.

“This is obviously a coordinated effort by the IRS to stifle these Tea Party and Tea Party-affiliated groups, and to stifle free speech activities,” ACLJ chief counsel Jay Sekulow told the New York Times.

ACLJ has posted some of the IRS demands on its website, including the questions being asked of Tea Party organizations.

One group, the Ohio Liberty Council, applied for tax-exempt status last year. The IRS has delayed its application and is currently seeking detailed information about the group, including a list of speakers from its events as well as printouts from its Facebook page.

“It’s intimidation, is what it is,” Tom Zawistowski, president of the Ohio Liberty Council, told the Cleveland Plain Dealer. “Is this the Soviet Union or the United States?”