President Donald Trump says he is considering “taking away” the U.S. citizenship of a longtime rival, actress and comedian Rosie O’Donnell, despite a decades-old Supreme Court ruling that expressly prohibits such an action by the government.

“Because of the fact that Rosie O’Donnell is not in the best interests of our Great Country, I am giving serious consideration to taking away her Citizenship,” Trump wrote in a social media post on Saturday. He added that O’Donnell, who moved to Ireland in January, should stay in Ireland “if they want her.”

The two have criticized each other publicly for years, an often bitter back-and-forth that predates Trump’s involvement in politics. In recent days, O’Donnell on social media denounced Trump and recent moves by his administration, including the signing of a massive GOP-backed tax breaks and spending cuts plan.

It’s just the latest threat by Trump to revoke the citizenship of people with whom he has publicly disagreed, most recently his former adviser and one-time ally, Elon Musk.

But O’Donnell’s situation is notably different from Musk, who was born in South Africa. O’Donnell was born in the United States and has a constitutional right to U.S. citizenship. The U.S. State Department notes on its website that U.S. citizens by birth or naturalization may relinquish U.S. nationality by taking certain steps – but only if the act is performed voluntary and with the intention of relinquishing U.S. citizenship.

Amanda Frost, a law professor at the University of Virginia School of Law, noted the Supreme Court ruled in a 1967 case that the Fourteen Amendment of the Constitution prevents the government from taking away citizenship.

“The president has no authority to take away the citizenship of a native-born U.S. citizen,” Frost said in an email Saturday. “In short, we are nation founded on the principle that the people choose the government; the government cannot choose the people.”

O’Donnell moved to Ireland after Trump defeated Vice President Kamala Harris to win his second term. She has said she’s in the process of obtaining Irish citizenship based on family lineage.

Responding to Trump Saturday, O’Donnell wrote on social media that she had upset the president and “add me to the list of people who oppose him at every turn.”