Two Senate Democrats wrote to a pair of federal agencies this week urging them to come up with recommendations for improving self-driving automobile software following a fatal crash involving a Tesla in Texas.

Sens. Ed Markey (D-Mass.) and Richard Blumenthal (D-Conn.) wrote in a letter to the National Highway Traffic Safety Administration (NHTSA) and the National Transportation Safety Board that the agencies should develop “recommendations for how automated driving and driving assistance systems like Tesla’s Autopilot can be improved,” and warned that fatal crashes involving self-driving car software are becoming a “pattern.”

“While automated driving and driver assistance systems — like the Autopilot feature on Tesla cars — can help prevent injurious and fatal accidents, they must be implemented strategically and safely,” reads the letter, obtained by The Hill.

“The most recent Tesla crash is the latest in a rash of accidents — the 28th — that NHTSA is investigating involving a Tesla car. We fear safety concerns involving these vehicles are becoming a pattern, which is incredibly worrisome and deserves your undivided attention,” it continues.

Their letter referred to a fatal crash that occurred over the weekend in Texas involving a Tesla that struck a tree after failing to make a turn; investigators have said that initial evidence indicates that no one was behind the wheel at the time of the crash, while Tesla CEO Elon Musk has claimed that the car involved did not have the brand’s signature self-driving feature.