Updated at 2 p.m. June 21 to include contributions to U.S. Rep. John Carter, R-Round Rock. The headline was updated to reflect that GEO is the top donor for three Texas congress members.

WASHINGTON -- One of the country’s largest operators of private immigration detention facilities has made significant contributions to several Texas members of Congress.

The GEO Group’s PAC and executives have given $32,900 to Houston Republican Rep. John Culberson’s campaign this election cycle, according to Federal Election Commission documents and OpenSecrets.org. GEO is Culberson's largest donor.

In Texas, GEO operates detention centers for Immigration and Customs Enforcement in Karnes City, Laredo, Pearsall and Conroe.

Culberson is facing a tough re-election race against Democrat Lizzie Fletcher. The race has been rated a ‘toss up’ by nonpartisan analyst Cook Political Report.

Culberson received the most funding from GEO out of Texas members of Congress, but GEO is also the top donor this cycle for U.S. Rep. Henry Cuellar, D-Laredo, who received $32,400, and Round Rock Republican Rep. John Carter, who received $31,600.

Both Culberson and Cuellar serve on the House Appropriations Homeland Security Subcommittee, which funds private immigration detention centers. Culberson is also the chairman of and Carter serves on the House Appropriations subcommittee on commerce, justice and science, which oversees funding for private prisons.

Cuellar’s campaign manager Colin Strother said that GEO is one of the largest employers in Cuellar’s district, and that Cuellar has not allowed campaign contributions to influence his decisions.

“If you live in a district in the state of Washington, you get boating money. If you live in a district in Nebraska, you get agriculture money. We have a district with lots of jail facilities that employ lots of people,” Strother said.

Culberson’s campaign did not respond to requests for comment.

GEO has also donated to other Texas lawmakers, including Republican Sen. John Cornyn, who received $10,000; House Committee on Homeland Security Chairman Rep. Michael McCaul, R-Austin, who received $2,500; Rep. Vicente Gonzalez, D-McAllen, who received $2,500; Rep. Kenny Marchant, R-Coppell, who received $1,000; and Rep. John Ratcliffe, R-Heath, who received $1,000. Republican Sen. Ted Cruz received $150.

GEO has come under scrutiny by immigrant rights organizations for alleged mismanagement and abuse in detention facilities. GEO faced class-action lawsuits in which detainees alleged that they were forced to work. In a GEO facility in California, three detainees died in custody. The American Civil Liberties Union accused GEO of denying detainees food, water and bathroom access.

"We strongly dispute these allegations. On a daily basis, our dedicated employees deliver high quality services, including around-the-clock medical care, that comply with performance-based standards set by the Federal government and adhere to guidelines set by leading third-party accreditation agencies," GEO said in a statement.

Another one of the largest groups that runs private immigration detention centers in the United States is CoreCivic. The company runs facilities in Houston, Laredo, Dilley and Taylor.

CoreCivic PACs have given less money to candidates than GEO, but still contributed to three Texans, according to OpenSecrets.org: Culberson with $11,000, McCaul with $3,500 and Cuellar with $1,500.

Washington correspondent Camille Caldera contributed to this report.