The Supreme Court has ruled that President Donald Trump can use $2.5 billion of Pentagon funds for a section of wall on the southern border.
There were five votes to four to block a ruling by a federal judge in California that barred President Trump from spending the money on the Mexican wall.
The wall, dividing the US and Mexico, was President Trump’s major campaign promise during the 2016 election.
The constructing of the wall is fiercely opposed by Democrats.
The decision by the Supreme Court means that the money will be used for wall projects in California, Arizona and New Mexico.
The court in California had argued that Congress had not specifically authorized the funds to be used for constructing the wall.
In a tweet, President Trump described the ruling as a “big victory”.
He tweeted: “Wow! Big VICTORY on the Wall. The United States Supreme Court overturns lower court injunction, allows Southern Border Wall to proceed. Big WIN for Border Security and the Rule of Law!”
President Trump has argued that a new wall would help to curb illegal immigration, which he says is fuelling crime and placing a strain on the economy.
Democrats say they are in favor of border security but the wall would be expensive and ineffective. They argue that President Trump has manufactured the border emergency and that the wall has become a symbol of Trump’s anti-immigration platform.
On July 26, the US and Guatemala signed a deal, under which migrants from Honduras and El Salvador who pass through Guatemala will be required to stop and seek asylum there first, rather than heading straight for the US.
The American Civil Liberties Union (ACLU) has vowed to seek an expedited decision from the Ninth Circuit Court of Appeals “to halt the irreversible and imminent damage from Trump’s border wall”.
President Trump declared an emergency earlier this year, saying he needed $6.7 billion to build the wall as a matter of national security. However, this figure is far short of the estimated $23 billion cost of a barrier along the whole 2,000 miles of border.
Democrats claimed President Trump’s decision to declare an emergency exceeded his powers under the US constitution.
About 20 states, along with groups including the ACLU have filed lawsuits to try and stop the president using the emergency declaration to bypass Congress.
The House of Representatives is also taking legal action to stop the diversion of further funds for the wall project.
According to US authorities, 104,344 people were arrested along the southwest border in June – a 28% drop from the previous month.
The Trump administration claims the decrease is due to new policies with Mexico to curb migration, including increased security on the Mexican side of the border, and the expansion of a scheme that makes asylum seekers wait in Mexico while their cases are being processed.
However, experts say that reduced migration is also typical during the hot summer months.
The number of people detained on the US-Mexico border is far lower when compared with the previous decade.
The number fell in President Trump’s first year but rose again in 2018 – but even before the increase, when migration numbers were at historic lows, Donald Trump described the situation on the border as a national security crisis.