The Justice Department sued Stephen Wynn, the former casino mogul, on Tuesday, seeking to force him to register as an agent of the Chinese government and saying he had made requests on the government’s behalf to Donald J. Trump when he was president.

According to the lawsuit, Mr. Wynn passed along a request to Mr. Trump in 2017 from the Chinese government to kick a Chinese national who had sought asylum in the United States out of the country.

By serving as a middleman for the Chinese government, Mr. Wynn acted as a foreign agent, the Justice Department said. The department said it had asked Mr. Wynn to register himself as a foreign agent under the Foreign Agents Registration Act by letter in 2018, 2021 and April of this year, but he had refused to do so.

“The filing of this suit — the first affirmative civil lawsuit under FARA in more than three decades — demonstrates the department’s commitment to ensuring transparency in our democratic system,” Matthew G. Olsen, assistant attorney general of the Justice Department’s national security division, said in a statement. “Where a foreign government uses an American as its agent to influence policy decisions in the United States, FARA gives the American people a right to know.”