Senate Minority Leader Chuck Schumer (D-NY) raised concerns over the US Army’s use of the Chinese-owned social media app TikTok to find recruits in a letter directed to the military branch’s top official last week, as first reported by BuzzFeed News.

“While I recognize that the Army must adapt its recruiting techniques in order to attract young Americans to serve,” Schumer wrote. “I urge you to assess the potential national security risks posed by China-owned technology companies before choosing to utilize certain platforms.”

In his letter, Schumer asks Army Secretary Ryan McCarthy whether the Army was in contact with intelligence officials over its decision to use the TikTok platform recruiting and if it “conducted an analysis of alternative recruiting platforms” before moving to do so. McCarthy has until December 6th to respond.

There’s been a broader movement in the Senate building over concerns that TikTok and its parent company, ByteDance, could threaten US national security or the privacy of American users. Last month, Schumer co-authored a letter to Director of National Intelligence Joseph Maguire with Sen. Tom Cotton (R-AR) asking that he investigate the company and determine whether it poses any security risks.

Sen. Marco Rubio (R-FL) demanded that the Committee on Foreign Investment in the United States (CFIUS) conduct a full review of TikTok’s acquisition of the app Muscal.ly, which led it to enter the US market. That investigation has reportedly begun, according to Reuters. One of the Senate’s leading China and tech hawks, Sen. Josh Hawley (R-MO), held a hearing last week aimed at analyzing TikTok’s relationship with the Chinese government. The company did not send someone to represent it.

“We appreciate Sen. Hawley’s invitation. Unfortunately, on short notice we were unable to provide a witness who would be able to contribute to a substantive discussion,” a TikTok spokesperson told The Verge at the time.