Letter to Tony Xu, CEO of DoorDash, Matt Maloney, CEO of Grubhub Inc., Apoorva Mehta, CEO of Instacart, Logan Green, CEO of Lyft, Bastian Lehmann, CEO of Postmates, and Dara Khosrowshahi, CEO of Uber - Sen. Warner Calls on Gig Worker Platform Companies to Offer Flexibility in the Event of Coronavirus Outbreak