United States President Donald Trump on Sunday said he would be willing to shut down the federal government if Democrats refuse to support changes to immigration laws.

“I would be willing to ‘shut down’ government if the Democrats do not give us the votes for Border Security, which includes the Wall!” Trump said in a tweet. “Must get rid of Lottery, Catch [and] Release etc. and finally go to system of immigration based on merit! We need great people coming into our Country!” the president said.

Trump wants Congress to pass legislation that addresses immigration issues, including the border wall along the US-Mexico border, changing the way visas are allotted and other immigration restrictions, ABC News reported. Trump also wants to end the practice of releasing immigrants caught entering the country illegally on the condition that they show up for court hearings. He has demanded that the US shift to an immigration system based more on merit and less on family ties.

However, a disruption in federal government operations could backfire on Trump if voters blame Republicans, who control Congress, for the interruption in services, Reuters reported.

The federal government has already shut down twice this year – first over a failed deal for the Dreamers programme that granted temporary legal status to undocumented immigrants, then over a funding bill in January. In May, Trump suggested “closing up the country for a while” if he did not get his wall, according to CNN.

The Republican president has focussed on tougher immigration laws during his administration, from the travel ban on people from predominantly Muslim nations to the separation of illegal immigrant children from their parents at the US-Mexico border. On Friday, a federal judge urged the government to focus on finding deported immigrant parents whose children remain in America, Reuters reported.