Ana Suda and Martha Hernandez were lining up to buy milk and eggs from Town Pump, a Le Havre convenience store, when a customs officer approached them.
CBP officer Paul O'Neal "selected, detained and interrogated" them because he had heard them speak Spanish, according to the complaint filed in the Great Falls US District Court.
The officer detained the two women for 40 minutes in a parking lot without reasonable suspicion or probable cause, says the lawsuit.
Suda filmed a video of the meeting with O'Neal on the parking lot, in which she asked him why he wanted their IDs.
The American Civil Liberties Union women's lawyers said the officer should have let them go as soon as they identified as US citizens.
The prosecution also claims that the officer targeted them because of their race.
Suda and Hernandez claim unspecified cash compensation, punitive damages and an order of a judge prohibiting border authorities from arresting or detaining anyone for reasons of race, accent or of language. CBP spokesman Jason Givens said Thursday.
Hernandeza said her 8-year-old daughter was afraid to speak Spanish in public after 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. Both are licensed practical nurses who work in a assisted living center.
