The US president said they should be immediately sent back to where they came from without any judicial process.
"Our Immigration policy, laughed at all over the world, is very unfair to all of those people who have gone through the system legally and are waiting on line for years!" the president added.
We can not allow all of these people to invade our Country. "When somebody comes in, we must immediately, with no Judges or Court Cases, bring them back from where they came", Trump said in a series of two tweets Sunday morning.
Trump's tough demand to end that legal process would face stiff opposition in Congress, which for years has been stalemated on changes to US immigration policies and unable to enact new migration laws.
The Republican-controlled House of Representatives is still planning to vote this week on comprehensive immigration policy changes after last week defeating a tougher version of new immigration controls.
In a pair of tweets sent while being driven to his Virginia golf course, Trump described immigrants as "invaders" and said United States immigration laws should be changed to take away trial rights from undocumented migrants. Leonard Lance, R-7th Dist., and Brendan Boyle, D-Pa., to propose legislation requiring the administration to reunite the families.
"What President Trump has suggested here is both illegal and unconstitutional".
The Trump administration has faced increasing criticism over what advisers have claimed is a conscious decision to take minors away from undocumented immigrant parents and guardians.
Merkel advocates bilateral, trilateral deals over migrants to EU
Migration has decided elections across the bloc from Italy to Hungary, with voters favoring those taking a tougher stance. They are considering setting up centers overseas to decide on asylum requests there and send back those whose cases fail.
The border patrol took 2,342 children from their parents from May 5 to June 9, according to the DHS.
"We're going to have strong, very strong borders, but we're going to keep the families together", Trump told reporters in the Oval Office prior to signing the directive.
Many of them were responding to the president's Friday tweet saying Republicans "should stop wasting their time" on immigration reform until they elect more lawmakers in a "Red Wave" this November.
He said it would address border security, protections for "Dreamers", family migration and the separation of children from their parents.
USA law does permit expedited deportations if an immigrant is apprehended within 160km of the border and has been in the country for less than 14 days. "There are already people being removed with a truncated process".
Senator James Lankford expressed confidence today in the efforts to get kids back with their families and the workers from DHS, HHS and other agencies that are handling the cases. But it has settled on a location for much of the activity: Port Isabel Service Processing Center, 20 miles northeast of Brownsville, Texas.
It says the government knows the location of all children in its custody and is working to return them to their parents.