Three top Democratic senators were working with the hotel industry when they wrote a letter to the Federal Trade Commission last year urging it to investigate Airbnb and others in the “sharing economy.”

The letter from Sens. Elizabeth Warren of Massachusetts, Dianne Feinstein of California and Brian Schatz of Hawaii was part of a coordinated, multipronged strategy by hotel lobbyists to use federal regulations to cripple Airbnb, which has emerged as a major competitor to the traditional hospitality industry.