AUSTIN, Texas (AP) — More than 40 congressmen have signed a letter calling on U.S. Immigration and Customs Enforcement to investigate its handling of sexual assault reports in its detention facilities.

The letter released Monday is based on the case of Laura Monterrosa, a detainee at the T. Don Hutto Residential Center in Central Texas. The FBI is investigating her allegation that a female guard assaulted her.

U.S. Reps. Joaquin Castro and Lloyd Doggett, both Democrats, wrote that they were concerned about the "prevalence of reports of sexual assault and abuse" in Texas immigration facilities.

The advocacy group Grassroots Leadership, which is working with Monterrosa, says detention center employees are pressuring her to recant her allegations. ICE says it "fully respects the rights of all people to voice their opinion without interference."