Immigration agents recently detained an undocumented grandmother after asking a Greyhound bus full of passengers for identification.

Greyhound buses are often used as a mode of transportation by working immigrants. They have recently become prime targets of immigration authorities. According to federal law, agents have the right to question immigration status if they have “reasonable suspicion”—but immigration activists are demanding limits to these open-ended rules.

“It’s not just immigrants,” activist Isabel Sousa-Rodriguez said. “At this point, anyone who’s riding a bus apparently, they need to know their constitutional rights.”