Two Montana women questioned by a U.S. border agent who overheard them speaking Spanish in a convenience store sued U.S. Customs and Border Protection on Thursday, saying the agent illegally detained them without reason.

In May, Ana Suda and Martha “Mimi” Hernandez were waiting in line to buy milk and eggs at the Town Pump, a convenience store in Havre, when a border agent approached them.

The CBP agent, Paul O’Neal, “singled out, detained and interrogated” them “because he heard them speaking Spanish,” according to the lawsuit filed in U.S. District Court in Great Falls.

The agent held Suda and Hernandez for 40 minutes in a parking lot without reasonable suspicion or probable cause, the lawsuit claims.

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Suda filmed a video of the parking lot encounter with O’Neal in which she's seen asking him why he wanted their identifications.

"Ma'am, the reason I asked you for your ID is because I came in here and I saw that you guys are speaking Spanish, which is very unheard of up here," O'Neal said in the video.

The women’s American Civil Liberties Union lawyers said the agent should have let them go as soon as they identified themselves as U.S. citizens, but he instead detained them in violation of the Fourth Amendment barring unreasonable searches and seizures.

The lawsuit also claims the agent targeted them based on their race in violation of the Fifth Amendment's due process protections.

“Agent O’Neal singled them out based on race, relying on their use of Spanish as a justification and proxy for race,” the lawsuit stated.

The ACLU wrote in a statement that the incident was humiliating for the two women who have been “shunned and harassed by other town residents.”

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Suda and Hernandez are asking for an unspecified amount of money in compensation, punitive damages and a judge's order barring border officials from stopping or detaining anyone based on race, accent or language. CBP spokesman Jason Givens said Thursday the agency doesn't comment on pending litigation.

Suda said in a statement that the incident “changed our lives, I believe, forever.” She said her 8-year-old daughter is afraid to speak Spanish in public following the incident, The Washington Post reported.

Suda was born in Texas and moved to Montana with her husband in 2014. Hernandez was born in California and has been living in Montana since 2010. The two are certified nursing assistants who work at an assisted-living center.

The Associated Press contributed to this report.