The D.C. Taxicab Commission says taxi and sedan service Uber is charging an automatic 20 percent tip on cab rides booked through its app or website, a practice the agency says is illegal, but one they can’t do anything about, the Washington Examiner reported.

The District’s top taxi regulator, Ron Linton, told cabbies last month that Uber shouldn’t be doing that and that he had asked them to stop. Uber says it doesn’t think the automatic tip is illegal.