“Fortunately, Congress — not the President — has the power of the purse, and my colleagues and I will not stand idly by as this Administration ignores congressional intent,” Engel said.
Engel cited a law known as the Impoundment Control Act, which he said prohibits the president from withholding or impounding money appropriated by Congress.
The lawmakers said his office has reached out to the Government Accountability Office – which is statutorily authorized to track acts of impoundment – to ensure that the president does not violate the law.
Earlier in the day, Trump that he has alerted the US military and Border Patrol of a national emergency after Mexico was unable to stop the caravan of migrants.
READ MORE: Trump Alerts Border Patrol, Military That Migrant Caravan is National Emergency
A caravan of 5,000 to 7,000 migrants from Honduras, Guatemala and El Salvador has crossed into Mexico en route to the United States, prompting multiple threats from Trump, who vowed in a Twitter post earlier on Monday to completely cut off or dramatically reduce foreign aid to the three Central American nations.