The Department of Homeland Security said in a statement the flights would transport Guatemalan, Honduran and Salvadoran migrant families who could not be immediately expelled under a coronavirus-related public health policy and did not have a legal basis to stay in the country.
"We are making clear that those who do not qualify to remain in the United States will be promptly removed," the statement said.
Migrant crossings typically taper off in the hot summer months, but arrests at the southern border rose in June to the highest level since April 2000. The tally in July is expected to be similar or even higher, according to two border patrol officials who spoke on the condition of anonymity.
Immigration, and particularly the arrival of asylum seekers at the U.S. southern border, has been a hot-button issue for decades. Multiple attempts to reform U.S. laws and create a pathway to citizenship for the millions of immigrants living in the country illegally have failed in Congress.