"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 HatchOvernight Finance: GOP releases spending bill | Dem senator threatens funding | Trump puts new target on businesses The Hill's 12:30 Report Hatch to meet with Trump Cabinet picks Thursday 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 McConnellSenate holds two-hour Biden lovefest Confirm Gary Richard Brown for the Eastern District of New York The Hill's 12:30 Report MORE (Ky.), Mike EnziMike EnziSenate Dems draw hard line over miners' pension bill Republicans want to grease tracks for Trump President-elect Trump: Please drain the student loan swamp MORE (Wyo.), Lamar AlexanderLamar AlexanderSenate sends far-ranging medical cures bill to Obama's desk It’ll take at least two years to repeal and replace ObamaCare GOP eager to see Harry Reid go MORE (Tenn.), John CornynJohn CornynDem senator threatens to slow-walk spending bill Ark., Texas senators put cheese dip vs. queso to the test Texan tackles tricky tongue twister for #TheEllieChallenge MORE (Texas), Kay Bailey Hutchison (Texas), Jon Kyl (Ariz.), Bob CorkerBob CorkerTrump's Cabinet: What jobs are left to fill Petraeus appointment could rankle wary FBI Haley to meet with senators during Washington trip MORE (Tenn.), Pat RobertsPat RobertsSenate GOP to Obama: Stop issuing new rules GOP debates going big on tax reform Memo to the LGBT community: Donald Trump is not your enemy MORE (Kan.), John ThuneJohn ThuneOvernight Tech: Senate probes AT&T Time Warner Merger | Time Warner to stand ground on Trump | Rep. Blackburn has FCC thoughts Overnight Tech: Big win for Samsung over Apple | Trump to sit down with tech leaders | Trump claims credit for B investment deal Senate Dems may block water bill over drought language MORE (S.D.) and Rand PaulRand PaulGOP rep: Trump has 'extra-constitutional' view of presidency The ignored question: What does the future Republican Party look like? Rand Paul skeptical about Romney as secretary of State MORE (Ky.).

— Bernie Becker contributed to this report.