SAN ANTONIO >> After tens of thousands of migrant families, most from Central America, crossed the Rio Grande into Texas last summer, the government poured millions of dollars into two large detention centers meant to hold women and children — and keep more from coming.

But as U.S. Immigration and Customs Enforcement expands the centers to make space for the next wave of arrivals, the agency faces legal and political challenges that could shut them down. And a new flow of migrants raises questions as to whether the strategy has deterred migration at all.

One center is a purpose-built, 50-acre campus in Dilley, an hour’s drive southwest of San Antonio. Another, smaller center is tucked among derricks in Karnes City. They will be able to house some 3,400 migrants once they reach full capacity, just a fraction of those crossing, leaving ICE with few options besides releasing many with notices to appear in court, as it did in the past.

Some 130 House Democrats and 33 senators have called on the government to halt family detention, while a federal judge in California has tentatively ruled that the policy violates parts of an 18-year-old court settlement that says immigrant children cannot be held in secure facilities. ICE responded by pledging to improve its centers while it awaits the judge’s ruling.

"We are moving in the direction of closing these centers down," said Jonathan Ryan, executive director of the Refugee and Immigrant Center for Education and Legal Services.

In April, Judge Dolly Gee tentatively ruled that family detention violates parts of a 1997 settlement in a case known as Flores V. Meese. The settlement stipulates migrant children must be released only to foster care, relatives or — if they must be held — in the least restrictive environment possible in facilities licensed to care for children.

Gee placed her ruling on hold and kept it secret so that government and immigration lawyers can try to negotiate a solution by mid-June. But a memo describing the ruling by Carlos Holguin, an attorney with the Center for Human Rights and Constitutional Law in California, says Gee agreed that the settlement applied to all minors in immigration custody, including those accompanied by a parent, and found the new detention facilities not licensed to care for children.

ICE director Sarah Saldana responded to the court in a statement saying that the agency would review cases of families detained more than 90 days, increase oversight and explore ways to improve conditions. "We understand the unique and sensitive nature of detaining families," she said.

In making its case for detention last year, the Department of Homeland Security argued that the centers were necessary to stamp out a widespread belief among migrants that the government was doling out "permisos" for them to stay, actually notices to appear in court.

According to the memo, Gee questioned whether the centers had served that purpose. Holguin wrote that the court found it "astonishing" that immigration authorities had adopted a policy demanding such expensive infrastructure without solid evidence that building it would discourage illegal migration. Nearly 17,000 families have already been caught at the border during the first seven months of this fiscal year, which began in October.

Family detention isn’t cheap. An ICE official said it costs $300 per day for each woman or child housed at Dilley. At a capacity of 2,400 people, it will cost the federal government $720,000 a day, or nearly $263 million a year. The smaller detention center in Karnes costs ICE $160 per detainee per day and is expected to have 1,000 beds by year’s end. The only other family detention center is in Berks County, Pennsylvania. For-profit prison operators manage all three facilities overseen by ICE.

Women with children caught entering the country illegally can be released or placed in detention. ICE says its decisions to detain or not depend on factors that include bed space and the ages and sexes of children.

The Texas centers provide considerable freedom of movement and boast amenities — Dilley has a huge indoor gym, soccer field and classrooms with touch-screen TVs and computers and the Karnes center has a library stocked with bilingual children’s books. But detainees would much rather have been released on the promise to show up in court, as happened to Jeysel Amaya.

Amaya, 24, said she left El Salvador because gang members "were threatening me and my sister, because my sister is 16 and (one) wanted to go with her."

In late April, she headed for the bus station in the border city of McAllen, her 4-month old daughter strapped to her chest in the same cloth sling she used throughout their 2,000-mile journey, and carrying a notice to show up in court near relatives in Los Angeles.