Senate Democrats sent a letter to President-elect Donald Trump on Tuesday calling on him to formally separate himself from his business interests in order to put all potential “ethical concerns” to rest.

The letter was signed by 23 Democrats, including Sen. Tom Carper, of Delaware, who is the top Democrat on the Senate Homeland Security and Governmental Affairs Committee. The group believes Trump’s business interests could create a serious conflict between Trump’s business interests and U.S. interests.