Los Angeles, California - California is set to sue the federal government on Wednesday over Donald Trump's on-again-off-again tariffs, claiming the president does not have the right to enact such damaging policies.

As the richest state in the union, and one of the country's largest importers and exporters, California looks set to bear the brunt of the economic damage forecasters expect from recent gyrations.

Democratic Governor Gavin Newsom – a long-time foe of Trump's and widely expected to be considering a 2028 presidential bid – will announce a lawsuit against the Republican administration, a statement said.

The legal action will argue that the International Emergency Economic Powers Act, which Trump has used to impose tariffs as high as 145%, does not grant him the authority to impose tariffs on goods coming into the US.

"President Trump's unlawful tariffs are wreaking chaos on California families, businesses, and our economy – driving up prices and threatening jobs," Newsom said in a statement.

"We're standing up for American families who can't afford to let the chaos continue."

The case is the latest of more than a dozen lawsuits that California has filed against the Trump administration, but it is the first one in which Newsom is taking such a prominent role.

The governor has spent much of the last three months trying to avoid open conflict with Trump.

After the fires that swept through Los Angeles in January, he went out of his way to welcome Trump and to impress upon him how much the state needed him.

But Trump's moves to stymie international trade could have a devastating effect on an economy that is hyper-exposed to the outside world, with huge volumes of trade passing through its ports, and millions of foreigners visiting every year.

Newsom's office says California – which would be the world's fifth largest economy if it were independent – could lose billions of dollars in revenue if Trump's tariff policies shrink international trade, especially with key trading partners China, Mexico, and Canada.