BOSTON — At least nine migrants, including six children, have died in federal custody since October, fueling calls for investigations of overcrowded conditions in detention centers on the U.S.-Mexico border.

Congressional lawmakers, including several from Massachusetts, have visited immigration centers in Texas and Florida, which have filled amid a record increase in people attempting to cross the border to enter the U.S.

Legislation by Rep. Lori Trahan, a Westford Democrat, would require Congress to be notified within 24 hours of a migrant's death while in federal custody and give broader authority to House committees to quickly hold hearings to investigate.

Her measure, which faces an uphill battle for approval, would also prevent Trump administration officials from claiming "executive privilege" to avoid testifying at those hearings.

"We want accountability for migrant deaths that happen in our custody," Trahan said at a briefing Tuesday. "We want to be notified within 24 hours and for that to trigger a public hearing so that people will come before a committee and account for not only what happened, but how we can prevent it from happening again."

Trahan visited detention centers in Texas on July 1 with members of the Congressional Hispanic Caucus. She said while it was obvious the facility had been cleaned in preparation for the official visit, she saw enough to convince her the "conditions are inadequate" and migrants are "not being treated with the humanity they deserve."

"It looked more like prison than a place where you would care for children," she said. "Trauma and despair were in the faces of everyone we saw."

Her proposal is backed by immigrant rights groups, who describe the conditions in the federal detention centers as "cruel and inhumane."

"What is happening at the border is horrific and unforgivable, and it will not stop until Congress holds the administration accountable," said Eva Millona, executive director of the Boston-based Massachusetts Immigrant Refugee Advocacy Coalition, which supports Trahan's bill. "Families shouldn't be hearing about the death of a child from the media."

Last week, the Department of Homeland Security inspector general’s office issued a scathing report citing "dangerous overcrowding" at temporary detention centers in Texas. The centers were built to house migrants before they are transferred to U.S. Immigration and Customs Enforcement for release or longer term detention.

Federal rules require children to be held by the Border Patrol for no longer than 72 hours before they are transferred to the custody of Health and Human Services, which houses migrant youth in facilities around the country. The Border Patrol must allow lawyers, doctors and other monitors to visit and interview children in its custody.

The Trump administration has been scrambling to find new space for immigrants amid criticism that the human rights of children are being violated.

Nearly 600,000 migrants have arrived at the U.S.-Mexico border since the federal fiscal year started in October, according to U.S. Customs and Border Protection data.

Acting Homeland Security Secretary Kevin McAleenan has appealed to Congress for more funding to address the surge.

Homeland Security officials have also ordered medical checks of all children in their custody and expanded medical screenings of migrants as they arrive at the border.

Even if the House takes up Trahan's bill this session, it would still need approval in the GOP-controlled Senate and Republican President Donald Trump's signature to become law. Trump has accused lawmakers and the media of reporting "phony and exaggerated accounts" of poor conditions at border detention centers.

Christian M. Wade covers the Massachusetts Statehouse for North of Boston Media Group’s newspapers and websites.