Bob Casey is picking his first battle with Donald Trump.

Pennsylvania’s senior Senator announced today that he is co-sponsoring the Presidential Conflicts of Interest Act of 2017.

The legislation, introduced by Senator Elizabeth Warren of Massachusetts, is aimed at Trump’s relationship with his business.

The President-Elect has refused calls to separate himself from the Trump Organization and even told the New York Times that “the president can’t have a conflict of interest.”

“President-elect Trump’s conflicts of interests are unprecedented and for the good of our nation he must divest himself from his businesses,” Senator Casey said. “The American people deserve to know that their President is acting in their best interest and not for the benefit of his business interests. Unless President-elect Trump divests, the American people will have no way of knowing where the Trump Organization ends and the Trump Administration begins.”

The legislation would also force Trump to release his tax returns, something he avoided during the campaign.

Since the bill is only supported by some Democratic members of the Senate, and they represent the minority party in the upper chamber, this legislation will likely never see the light of day.