The Washington Post has a story about how two Spanish-speaking American citizens were detained and questioned for 35 to 40 minutes in a convenience store parking lot in Havre because the agent overheard them speaking Spanish.
One of the women filmed part of the encounter on her cell phone. When she asked the agent why he wanted to see their IDs, he answered: “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.”