Participating carriers are not required to make contract fares available to such users, but may do so at their option. ... Agency 10 Letter AIRLINE PAYMENT METHOD Required Air Cal GTR. cash or personal credit card YES Alaska GTR YES Branifl ... YES SAMPLE AGENCY LETTER OF IDENTIFICATION (To be typed on agency official letterhead) TO: GSA Contract Airline ... The employee is thereby eligible and authorized to use the GSA contract discount fares in accordance with youranbsp;...