After congressional Republicans repeatedly failed last year to repeal the Affordable Care Act, President Trump promised to “let Obamacare implode” on its own.

A new lawsuit being filed Thursday argues that Trump’s efforts to make good on that promise violate the U.S. Constitution.

Trump has “waged a relentless effort to use executive action alone to undermine and, ultimately, eliminate the law,” the complaint charges, according to a draft obtained by NBC News. The lawsuit is being filed in Maryland federal court by the cities of Chicago, Columbus, Cincinnati and Baltimore.

Since his first executive order directing federal agencies to claw back as much of the Affordable Care Act as possible, Trump’s directives have increased health coverage costs and depressed enrollment, the complainants say.

Specifically, the suit argues that Trump is violating Article II of the Constitution, requiring the president to “take care that the laws be faithfully executed.”