"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: US preps cases linking North Korea to Fed heist | GOP chair says Dodd-Frank a 2017 priority | Chamber pushes lawmakers on Trump's trade pick | Labor nominee faces Senate US Chamber urges quick vote on USTR nominee Lighthizer Live coverage: Day three of Supreme Court nominee hearing 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 McConnellThe Memo: Winners and losers from the battle over health care GOP senators pitch alternatives after House pulls ObamaCare repeal bill Under pressure, Dems hold back Gorsuch support MORE (Ky.), Mike EnziMike EnziTop Dem: Trump's State Dept. cuts a 'Ponzi scheme' Republicans eye strategy for repealing Wall Street reform Lawmakers fundraise amid rising town hall pressure MORE (Wyo.), Lamar AlexanderLamar AlexanderOvernight Regulation: Trump's Labor nominee hints at updating overtime rule Trump's Labor pick signals support for overtime pay hike Live coverage: Day three of Supreme Court nominee hearing MORE (Tenn.), John CornynJohn CornynGOP senators pitch alternatives after House pulls ObamaCare repeal bill Rand Paul takes victory lap on GOP health bill Senators push Trump on defense deals with India MORE (Texas), Kay Bailey Hutchison (Texas), Jon Kyl (Ariz.), Bob CorkerBob CorkerGOP lawmaker: Time to work with Dems on healthcare GOP senator: I'm ready to work with Trump, Dems on healthcare Senators introduce new Iran sanctions MORE (Tenn.), Pat RobertsPat RobertsDems mock House GOP over lack of women in healthcare meeting Perdue vows to be chief salesman for US agriculture abroad GOP senator apologizes for mammogram joke MORE (Kan.), John ThuneJohn ThuneLawmakers want infrastructure funded by offshore tax reform Senate GOP hedges on ObamaCare repeal timeline Week ahead: Robocall crackdown tops FCC meeting agenda MORE (S.D.) and Rand PaulRand PaulTrump, GOP fumble chance to govern GOP senators pitch alternatives after House pulls ObamaCare repeal bill Rand Paul takes victory lap on GOP health bill MORE (Ky.).

— Bernie Becker contributed to this report.