A group comprised of former White House ethics lawyers and constitutional law scholars are alleging that Trump has contravened the Emoluments Clause by accepting payments to his many businesses from foreign governments, reports the New York Times.

Citizens for Responsibility and Ethics in Washington, the group behind the legal effort, seeks to block Trump from receiving such payments to his businesses without Congressional approval.

The group fears that Trump’s sprawling global empire of hotels and other businesses and his functioning as U.S. President could become entangled otherwise. According to CNN, Trump is linked to over 500 entities with businesses in at least 25 countries outside the U.S.

“We did not want to get to this point,” executive director Noah Bookbinder said in a press release. “It was our hope that President Trump would take the necessary steps to avoid violating the Constitution before he took office.”

Earlier this month, Trump announced plans to avoid any conflicts of interest while he is in office, in part by refraining the Trump Organization from making overseas business deals. According to one of his lawyers, the President will transfer his assets into a trust run by his sons, Donald Jr. and Eric.

Eric Trump, an executive vice president at the Trump Organization, told the Times that the lawsuit is “purely harassment for political gain” and “sad.”

For more on Donald Trump’s potential conflicts of interest, watch Fortune’s video:

Citizens for Responsibility and Ethics in Washington is far from the only group scrutinizing the potential intertwining links between Trump’s businesses and his behavior in office. Calling this a “good government issue,” Senator Elizabeth Warren introduced a bill earlier this month which, while largely symbolic, would have required the President and Vice President to sell their business interests.