"The privacy interests of donors is widely recognized and valued. Various public policy initiatives have rightly encouraged donations to social welfare organizations, and these efforts are threatened when private information about donors is not adequately protected," the letter states.

The new letter, from Sen. Orrin HatchOrrin HatchTrump, GOP set to battle on spending cuts GOP eyes new push to break up California court Overnight Defense: Senate to vote on defense picks Friday | 41 detainees left at Gitmo | North Korea may be prepping missile launch MORE (R-Utah) and other GOP senators, says that, by requesting the confidential donor names, the agency has set in motion a process that will result in the names being available for public viewing at the IRS when the investigated groups are approved to become a 501(c)(4).

"The IRS appears to be circumventing the statutory privacy protections that Congress has long provided donors," exposing the donors to "possible harassment," the Republicans said."The public release of private donor information exposes citizens to possible harassment and intimidation by those who oppose the goals of the charitable organization."

Republicans and Democrats on Capitol Hill have been clashing over 501(c)(4) and other tax-exempt groups, some of which are spending millions of dollars this year on election advertising. 

The IRS currently says that the primary purpose of 501(c)(4) groups should not be political, which has led some legal analysts to assert that those organizations should use less than 50 percent of their budget on political causes.  

Watchdogs argue groups are misusing the 501(c)(4) tax-exempt status to keep their donors secret as they spend millions on election ads. 

The Republican senators requested that the IRS provide the statutory authority to require donor names, the frequency of requests for the information, and which officials were involved in requesting and approving the "questions requesting donor names," among other issues.

Along with Hatch, the Republican senators who signed the letter were Mitch McConnellMitch McConnellPanel to vote on Trump’s Transportation nominee Tuesday This week: Congressional Republicans prepare to huddle with Trump Trump to meet with congressional leaders Monday: report MORE (Ky.), Mike EnziMike EnziDem senator: DeVos ‘sends shivers down the spine’ Trump Education pick: States should decide on allowing guns in schools Schumer puts GOP on notice over ObamaCare repeal MORE (Wyo.), Lamar AlexanderLamar AlexanderTrump, GOP set to battle on spending cuts Senate committee vote on DeVos postponed Cheney calls for DeVos to be confirmed ‘promptly’ MORE (Tenn.), John CornynJohn CornynThis week: Congressional Republicans prepare to huddle with Trump GOP eyes new push to break up California court Senate confirms first nominees of Trump era MORE (Texas), Kay Bailey Hutchison (Texas), Jon Kyl (Ariz.), Bob CorkerBob CorkerRubio to vote for Tillerson Top Dem comes out against Tillerson ahead of key vote This week: Congressional Republicans prepare to huddle with Trump MORE (Tenn.), Pat RobertsPat RobertsOvernight Finance: Scoop – Trump team eyes dramatic spending cuts | Treasury pick survives stormy hearing Hearing derailed after senator suggests colleague needs Valium Live coverage: Senators grill Trump's Treasury pick MORE (Kan.), John ThuneJohn ThuneTrump, GOP set to battle on spending cuts Week ahead: FCC soon to be in Republican Pai's hands Senate confirms first nominees of Trump era MORE (S.D.) and Rand PaulRand PaulDems blast Trump plans for deep spending cuts Trump team prepares dramatic cuts Paul, Lee call on Trump to work with Congress on foreign policy MORE (Ky.).

— Bernie Becker contributed to this report.