Like the old established carriers, southwest was a unionized airline; about 84 percent of its employees belonged to a labor organization. Southwest negotiated contracts with a variety of unions, each representing district classes of employees : the teamsters represented airline mechinics, stock clerks and aircraft cleaners; the international association of machinists represented customer service and reservation employees; the transport workers union represented flight attendant; the southwest airline pilots association represented pilots, and the ramp operations and provisioning association represented baggage handlers.