MADRID, Dec 14 (Reuters) - Unions representing ground service workers at Spanish airports plan to call a strike between late December and early January, Iberia, part of the International Airlines Group, has announced.

The country's two main unions, UGT and CCOO, have called workers to strike between Dec. 29 and Jan. 7, Iberia said in a statement Wednesday night, adding that the call is "irresponsible" and "senseless."

"A strike such as the one now called by the unions for Christmas irreparably damages the right to vacations and the reunification of families and friends on such important dates," Iberia said.

Workers in ground services, such as baggage handling, at Spain's commercial airports, all run by state-owned Aena, are protesting against new contracts signed recently.

Aena has contracted new companies for these services, previously provided by Iberia at many airports, which has angered the unions, although the new companies have pledged to maintain the workers and their working conditions.

Iberia has appealed the new contracts in court.

(Reporting by Inti Landauro and Jakub Olesiuk; edited in Spanish by Javi West Larrañaga)