Representatives for Uber and Lyft told California state regulators on Tuesday that sharing ride-hailing data with public agencies—even if that information is anonymized or reported in aggregate—threatens the privacy of both riders and drivers.

Joe Okpaku, vice president of governmental relations for Lyft, testified at a state Public Utilities Commission workshop in San Francisco that data-crunchers can “reverse-engineer” ZIP code-level data and combine it with other publicly available information to determine where somebody lives, worships, works or goes to school. He cited published reports showing how researchers said they uncovered detailed information about customers of New York City taxis and Netflix despite efforts to mask their data.