Labour unions representing ground service workers at Spanish airports plan to strike from late December into early January, Spain's Iberia, part of the International Airlines Group, said.

The country's two main unions UGT and CCOO have called on workers to walk out between Dec. 29 and Jan. 7, Iberia said in a statement on Wednesday evening, adding the call is "irresponsible" and "makes no sense".

"A strike, like the one called by unions for Christmas hurts irremediably the right to holiday and reunite with families and friends," Iberia said.

Workers of ground services, such as baggage handling, at Spanish commercial airports, all of which are operated by state-controlled Aena, are protesting against new contracts recently signed.

They threatened to walk out on Dec. 5 and Dec. 10 though eventually called those strikes off. The two unions did not immediately respond to requests for comment.

Aena hired new contractors for the services, which were previously provided by Iberia in many airports, angering unions, even as the new contractors have committed to retain workers and their working conditions.

Iberia is challenging the new contracts in courts. (Reporting by Inti Landauro and Jakub Olesiuk)