The fatal crash of a Tesla in Texas over the weekend has prompted two U.S. senators to urge federal regulators to take action. “We fear safety concerns involving these vehicles are becoming a pattern, which is incredibly worrisome and deserves your undivided attention,” Sen. Richard Blumenthal (D-CT) and Sen. Ed Markey (D-MA) wrote to the National Highway Traffic Safety Administration, according to The Wall Street Journal. They asked the agency, which has investigated two dozen Tesla crashes, to come up with a plan for making Tesla’s Autopilot and other driver-assistance systems safer. Tesla boss Elon Musk claims Autopilot wasn’t engaged when a Tesla Model S crashed in a suburb of Houston Saturday, killing two men—but police said when they got to the mangled wreck, there was no one in the driver’s seat.