Six labor unions announced Thursday their endorsement of former city Managing Director Kirk Caldwell for Honolulu mayor.

Collectively, the unions represent about 7,200 current and retired workers from a cross-section of construction and building industries.

Endorsements were announced by the Plumbers & Fitters Local 675, International Brotherhood of Electrical Workers Local 1186, Elevator Constructors Local 126, Insulators and Allied Workers Local 132, Boilermakers Local 627 and Iron Workers Local 625.

"Our history of working with Kirk as managing director and (acting) mayor has been very positive and productive for the working families and members of our unions and we support Kirk Caldwell for mayor," said Reginald Castanares, business manager and financial secretary for the plumbers union.

Caldwell is running against incumbent Mayor Peter Carlisle and former Gov. Ben Cayetano.

The six unions also endorsed Caldwell in his unsuccessful run for mayor in 2010. Union leaders said they did not interview either of the other candidates in making their choice this year.

Caldwell also has been endorsed by the Hawaii Government Employees Association, the United Public Workers, the State of Hawaii Organization of Police Officers and the Hawaii Fire Fighters Association.