"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 Grant HatchGOP eyes limits on investor tax break Children’s health-care bill faces new obstacles Overnight Finance: White House requests B for disaster relief | Ex-Equifax chief grilled over stock sales | House panel approves B for border wall | Tax plan puts swing-state Republicans in tough spot 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 McConnellAddison (Mitch) Mitchell McConnellGun proposal picks up GOP support Children’s health-care bill faces new obstacles Dems see Trump as potential ally on gun reform MORE (Ky.), Mike EnziMichael (Mike) Bradley EnziThis week: Congress gets ball rolling on tax reform How the effort to replace ObamaCare failed Senate GOP budget paves way for .5T in tax cuts MORE (Wyo.), Lamar AlexanderAndrew (Lamar) Lamar AlexanderChildren’s health-care bill faces new obstacles Overnight Health Care: Schumer calls for tying ObamaCare fix to children's health insurance | Puerto Rico's water woes worsen | Dems plead for nursing home residents' right to sue Schumer calls for attaching ObamaCare fix to children's health insurance MORE (Tenn.), John CornynJohn CornynGun proposal picks up GOP support House bill set to reignite debate on warrantless surveillance Republicans jockey for position on immigration MORE (Texas), Kay Bailey Hutchison (Texas), Jon Kyl (Ariz.), Bob CorkerRobert (Bob) Phillips CorkerDeficit hawks voice worry over direction of tax plan The Hill Interview: Budget Chair Black sticks around for now Overnight Finance: White House requests B for disaster relief | Ex-Equifax chief grilled over stock sales | House panel approves B for border wall | Tax plan puts swing-state Republicans in tough spot MORE (Tenn.), Pat RobertsCharles (Pat) Patrick RobertsThe Hill's Whip List: Republicans try again on ObamaCare repeal No. 2 Senate Republican backs McConnell in Trump fight Overnight Healthcare: McConnell warns Senate not to block repeal debate | Insurers knock Cruz proposal | WH tries to discredit CBO | Lawmakers propose .1B NIH funding boost MORE (Kan.), John ThuneJohn Randolph ThuneGun proposal picks up GOP support Overnight Regulation: Senate panel approves driverless car bill | House bill to change joint-employer rule advances | Treasury to withdraw proposed estate tax rule | Feds delaying Obama methane leak rule Dems see Trump as potential ally on gun reform MORE (S.D.) and Rand PaulRandal (Rand) Howard PaulHouse bill set to reignite debate on warrantless surveillance Authorizing military force is necessary, but insufficient GOP feuds with outside group over analysis of tax framework MORE (Ky.).

— Bernie Becker contributed to this report.