A Montana woman said she plans to take legal action after a Border Patrol agent detained and questioned her and a friend – both U.S. citizens – after overhearing them speak in Spanish at a gas station.

The incident occurred early Wednesday morning at a convenience store in Havre, Montana, a town in the northern part of the state, near the border with Canada.

Ana Suda said she and her friend, Mimi Hernandez, were making a midnight run to the store to pick up some eggs and milk. Both are Mexican American and fluent in Spanish, and they were chatting in Spanish while waiting in line to pay when a uniformed Border Patrol agent interrupted them, Suda said.