Last week, two US citizens were asked for their IDs and detained by a border patrol agent after he heard them speaking Spanish in a gas station.

A video of the incident went viral and forced Customs and Border Protection to respond.

One of the women detained is joining forces with the American Civil Liberties Union to file a racial profiling lawsuit.

US Customs and Border Protection (CBP) is facing a potential lawsuit over a May 16 incident during which two Montana women, both US citizens, were detained after a border patrol agent heard them speaking Spanish.

Ana Suda and her friend Mimi Hernandez told The Washington Post they stopped at a gas station in Havre, Montana a little after midnight to pick up eggs and milk. Havre is a small town about 35 miles south of the Canadian border.

While border patrol agents are permitted to operate within 100 miles of borders, agents must have "reasonable suspicion" of an immigration-related crime to stop or detain someone.

The women were talking to each other in Spanish while waiting to check out at the gas station when a border patrol agent in line behind them stopped the women and asked to see their IDs.

The interaction continued in the parking lot, at which point Suda began filming the encounter. The video of the incident, which subsequently went viral, shows the two women asking the unidentified border patrol agent why he had asked for their IDs and detained them.

The agent can be heard saying in the clip, "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."

Suda directly asked if they were being racially profiled.

"It has nothing to do with that," the agent responded. "It's the fact that it has to do with you guys speaking Spanish in the store, in a state where it's predominantly English-speaking."

The interaction stayed relatively civil and the women were relased around 1 a.m., but the incident sparked outrage across the internet.

Speaking before the House Subcommittee on Border and Maritime Security, acting Border and Customs Protection commissioner Ronald Vitiello told lawmakers he was aware of the incident and had referred the case for disciplinary review.

"Bottom line, we expect our people to act with professionalism, and when they don't, we're going to hold them accountable for that," he said.

Suda, however, told several media outlets she intends to work with the American Civil Liberties Union to file a lawsuit against the border patrol.

The ACLU stated in a tweet on Monday, "Speaking Spanish is not a valid reason for Border Patrol to question or detain you. The Constitution prohibits all law enforcement agencies, including @CBP, from racial profiling and arbitrary searches and detentions."

An attorney with the ACLU's Border Rights Center confirmed to The Washington Post that she was in contact with Suda about the process of taking legal action.