The White House has sent a letter to the head of the Office of Government Ethics challenging his legal authority to demand the names of former lobbyists who have been granted waivers to work in President Trump’s administration. The highly unusual move, if successful, would make it impossible to know which, if any, officials are violating federal ethics rules. “It is an extraordinary thing,” said Walter M. Shaub, Jr., the head of the ethics office. “I have never seen anything like it.” Shaub is in his final year of a five-year term. He was appointed by President Obama, and he said he has no plans to back down. “It challenges the very authority of the director of the agency and his ability to carry out the functions of the office,” said Marilyn L. Glynn, who served as general counsel and acting director of the agency during the tenure of President George W. Bush. She called the move by the current White House “unprecedented and extremely troubling.”