President Donald Trump has appealed a federal judge ruling Friday that prohibits using $2.5 billion in military funds for his border wall with Mexico.

The U.S. District Court of Northern California struck down the $2.5 billion for the purpose of being used for the wall in California, New Mexico and Arizona.

At a press conference at the G20 summit in Osaka, Japan, Trump said, "we're immediately appealing it and we think we will win an appeal." The appeal will be made to the 9th Circuit Court of Appeals.

The wall has been the signature issue of Trump's border policy and a major promise during his 2016 presidential campaign. Trump had even stated during the campaign that he would have Mexico pay for the wall.

After the White House failed to win funding from Congress earlier this year, Trump declared a national emergency to obtain $6.7 billion to build the wall. Trump had originally attempted to use a government shutdown to pressure congressional Democrats.

There have been 16 states to file lawsuits challenging the emergency declaration, due to constitutional concerns.  

In the meantime, the Trump administration has pressured Mexico to strengthen border protection. The U.S. Acting Head Of Homeland Security Kevin McAleelan said Friday that border crossings are expected to be down 25% this month.

When asked by reporters if this is just due to the warm weather, he replied that Trump's border policy "is making an impact."

Congress on Thursday sent a $4.6 billion care bill meant to assist the tens of thousands of migrants at the U.S. border. Speaker of the House Nancy Pelosi was disappointed, as the bill did not include additional protections and accountability measures to help protect migrant children.