NASHVILLE (AP) - Tennessee senators Lamar Alexander and Bob Corker are among 12 Republican senators who are questioning whether the Obama administration is using the Internal Revenue Service to target tea party-related nonprofit organizations.

The dozen sent a letter Wednesday to IRS Commissioner Douglas Schulman seeking assurances that the agency's recent string of inquiries into some tea party-affiliated nonprofits is not based on politics.

The letter says the senators have received complaints of excessive IRS inquiries from organizations in Tennessee, Kentucky, Ohio and Texas.

"The extra scrutiny the IRS appears to be giving tea-party related nonprofits is disturbing, so I hope we find that the IRS is treating all tax-exempt organizations the same," Alexander said in a statement. "The government should not have what amounts to an enemies list based on what people or organizations say or believe, and if it turns out the IRS is denyi ng tea party groups the proper tax status because of what they have to say, it must stop and those responsible most be held accountable."

A spokesman for the IRS did not immediately return a phone call to The Associated Press seeking comment.

The organizations have been complaining that the IRS is purposely trying to thwart their attempts at achieving tax exempt status.

The organizations are applying under section 501(c)(4) of the federal tax code, which grants tax-exempt status to nonprofits for the promotion of social welfare. The 501 501(c)(4)s can engage in lobbying and political campaigning, but don't have to disclose who is donating money to them.

In addition to Alexander and Corker, the other senators who signed the letter were: Mitch McConnell and Sen. Rand Paul, both of Kentucky, Orrin Hatch, (Utah), Rob Portman (Ohio), Chuck Grassley (Iowa), Pat Roberts (Kan.), John Cornyn (Texas), Kay Bailey Hutchison (Texas), John Kyle ( Ariz.), and John Tune (S.D.)