The state of California filed a lawsuit on Wednesday against President Trump's proposed plan for a wall along the U.S.-Mexico border.

Xavier Becerra Xavier BecerraOVERNIGHT ENERGY: Trump casts doubt on climate change science during briefing on wildfires | Biden attacks Trump's climate record amid Western wildfires, lays out his plan | 20 states sue EPA over methane emissions standards rollback 20 states sue EPA over methane emissions standards rollback Investigation underway after bags of mail found dumped in Los Angeles-area parking lot MORE, the state's attorney general, announced in a statement that he has filed the lawsuit in the U.S. District Court for the Southern District of California.

The lawsuit argues that the Department of Homeland Security improperly waived the National Environmental Policy Act and other laws pertaining to immigration and the environment to expedite construction of the border wall in two California counties.

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The lawsuit also claims that the DHS violated the 10th Amendment of the Constitution and the separation of powers doctrine.

"The Trump administration has once again ignored laws it doesn't like in order to resuscitate a campaign talking point and build a wall on our southern border," Becerra said in the statement. "President Trump has yet to pivot from candidate Trump to a leader of a nation built on the rule of law. That's dangerous."

It's just the latest fight to erupt over Trump's signature campaign issue.

During the 2016 race, Trump repeatedly promised that the U.S. would build a wall on the southern border, with Mexico picking up the tab. Trump's supporters frequently chanted "build the wall" at his rallies.

But Mexican President Enrique Peña Nieto has repeatedly said that Mexico will not pay for the construction of the wall.

Congress has yet to fully fund the construction of the wall. Trump did not insist that the funding be included in the deal struck earlier this month to fund the government through December.

But the White House has made clear it's not giving up on the project.

Trump and Vice President Pence, in a series of promoted Facebook ads this week, state unequivocally that the wall will be built.

"There's been a lot of noise and a lot of rumors," reads the ad on Trump's personal Facebook page.

"WE WILL BUILD A WALL (NOT A FENCE) ALONG THE SOUTHERN BORDER OF THE UNITED STATES," it adds, calling the issue "non-negotiable."

- This story was updated at 2:45 p.m.