U.S. Sens. Jack Reed, of Rhode Island, and Richard Blumenthal, of Connecticut, are among the 13 Democrats planning to visit McAllen, Texas on Friday.
Vice President Mike Pence visited McAllen last week, where hundreds of men were crowded in sweltering, foul-smelling pens without cots on the concrete floor.
Pence's tour was meant to show the administration is providing adequate care for migrants but needs more money.
The scene he witnessed, though, sparked new criticism of the conditions facing migrants.
Top Senate Democrat Chuck Schumer of New York is also scheduled to make the trip Friday.
Reed and Blumenthal say they want to inspect the conditions in person.
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