The Justice Department sued longtime Las Vegas casino mogul Steve Wynn on Tuesday to compel him to register as a foreign agent because of lobbying work it says he performed at the behest of the Chinese government during the Trump administration.

The department said it had advised Wynn repeatedly over the last four years to register under the Foreign Agents Registration and is suing now because Wynn refused to do so.

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Though the Justice Department has ramped up efforts to criminally prosecute people who don’t register as foreign agents, officials described this case as the first lawsuit of its kind in more than three decades.

The complaint alleges that Wynn, who stepped down from his company, Wynn Resorts, in 2018 after multiple women accused him of sexual misconduct, lobbied then-President Donald Trump and members of his administration for several months in 2017 to remove from the United States a Chinese national who had been charged with corruption in China and was seeking political asylum in America.

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It says the lobbying effort was done on behalf of senior Chinese government officials, including Sin Lijun, the then-vice minister of the Ministry of Public Security, and included conversations over dinner with Trump and by phone.

Wynn’s lawyers said Tuesday that they would contest the suit.

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“Steve Wynn has never acted as an agent of the Chinese government and had no obligation to register under the Foreign Agents Registration Act,” said a statement from attorneys Reid Weingarten and Brian Heberlig. “We respectfully disagree with the Department of Justice’s legal interpretation of FARA and look forward to proving our case in court.”