Sixteen states in the United States of America have filed a lawsuit against President Donald Trump’s national emergency declaration, to fund his promised wall along the country’s border with Mexico.

The suit filed in US District Court for the Northern District of California on Monday, came as thousands of people rallied nationwide to protest against the Republican's move last week.

In a statement, California Attorney General Xavier Becerra, said the lawsuit alleges the Trump administration's action violates the Constitution.

Becerra said Trump knows there is no border crisis in the US, and also that his emergency declaration is unwarranted, and he admits that he will likely lose this case in court.