House and Senate Republicans are calling for an end to members’ use of the controversial TikTok video app for “official communications.”

Sen. Thom Tillis of North Carolina and Rep. Daniel Crenshaw of Texas lead a group of more than a dozen GOP members of the House and Senate agitating for a congressional rule change to ban members from using the app in an official capacity as members of Congress, though they could still use it for personal or campaign purposes.

“Some members of Congress who regularly use the app have minimized the security threat to our nation,” the lawmakers wrote Monday in a letter to leaders of the Senate Committee on Rules and Administration and the Committee on House Administration. “[But] there are several popular social media apps that are not at the same risk for the potential transfer of sensitive, private information to an adversarial foreign government.”

They also advocate for any appropriate measures “to mitigate the risks of this de-facto, spyware app,” the letter continues.

Congress, the White House, the U.S. military and more than half of U.S. states have already banned the app from official devices, citing security risks and the alleged mining of user data by ByteDance, the Beijing-based company that owns TikTok. Several other countries and the European Union have enacted similar bans of the app.

The Associated Press recently estimated that around two dozen lawmakers — all Democrats — still use the app from personal devices. Some have amassed sizable followings and use the platform to communicate with constituents. North Carolina freshman Rep. Jeff Jackson has 1.6 million TikTok followers and estimates that he reaches about 200,000 constituents who use it. The video-sharing app is used by about 150 million Americans daily.

The Biden administration is considering whether to force ByteDance to sell the social media app. China’s Commerce Ministry said last month that it opposes a forced sale.

TikTok CEO Shou Zi Chew was grilled last month at a House Energy and Commerce Committee hearing about the app’s relationship to the Chinese Communist Party, its handling of American user data and the alleged harm caused by its algorithm, which some say worsens the mental health of teenagers, particularly adolescent girls.

A flurry of legislation has been introduced in recent months to either impose an outright ban of the app or allow sanctions on companies like TikTok. Support for a ban or further restrictions has been largely bipartisan, though some Democrats, like Reps. Alexandria Ocasio-Cortez and Jamaal Bowman, both of New York, are among those who oppose a ban.

Jackson said he would support a ban in the event a sale is not possible. In the meantime, he told Roll Call he plans to continue using the app to reach his constituents, a practice that has rankled Tillis, his fellow North Carolinian.

Tillis issued a statement March 23 about “reckless” use of the app. He didn’t mention Jackson by name, but linked to an article about Jackson’s social media use.

Tillis struck a similar tone in the letter, citing recent warnings about data security from the Senate’s chief information officer and the House chief administrative officer.

“It is troublesome that some members continue to disregard these clear warnings and are even encouraging their constituents to use TikTok to interface with their elected representatives — especially since some of these users are minors,” the lawmakers wrote. “We feel this situation warrants further action to protect the privacy of both sensitive congressional information and the personal information of our constituents.”