Feb 13 (Reuters) -

Alaska Air flight attendants authorized a strike mandate for the first time in three decades, as thousands of cabin crew across three unions picket for higher pay outside airports in the United States, the UK and Guam on Tuesday.

The protests include cabin crew members from 24 airlines including Alaska, Southwest Airlines, United Airlines and American Airlines, picketing outside 30 airports.

U.S. flight attendants are unlikely to walk off the job because of a complex labor process that makes it difficult for airline workers to strike. But the first Alaska mandate since 1993 reflects labor's broader demands for higher pay at a time when a majority of U.S. cabin crew are in contract talks, the Association of Flight Attendants said.

While pilots across major airlines have secured new labor deals including bumper pay hikes and other benefits, some flight attendants have not had a pay raise in five years, the AFA said.

Flight attendants from Southwest Airlines and Air Transat in Canada, which are both pressing for steep pay raises, are in negotiations after rejecting earlier deals.

According to a February 9 union memo to Transat flight attendants seen by Reuters, an advisor assigned by the union is "no longer at the bargaining table," after members rejected two earlier agreements.

The Canadian Union of Public Employees (CUPE), which represents Transat flight attendants, said the change is related to internal union management, and would not impact the continuity of the negotiations. (Reporting by Shivansh Tiwary in Bengaluru, Allison Lampert in Montreal and Rajesh Kumar Singh in Chicago; Editing by Shinjini Ganguli)