So far more than 20,000 migrants have been returned all along the border to wait in Mexico, Mexican officials say.
The vice president visited the McAllen Border Station, where he was taken to a sweltering outdoor portal where 384 men were held in a caged area.
'I'm going to start showing some of these detention centres to the press. I want the press to go in and see them,' US President Donald Trump said.
On April 16, Attorney General Bill Barr directed immigration judges to no longer allow asylum-seekers apprehended after entering the country illegally to post bail.
Trump signed the bill in the Oval Office, flanked by Vice President Mike Pence and Health and Human Services Secretary Alex Azar.
The bill contains more than USD 1 billion to shelter and feed migrants detained by the border patrol and almost 3 billion dollars to care for the unaccompanied migrant children.