Spanish air traffic controllers are to strike over four days in July in a dispute over penalties given by airport operator AENA to controllers for a strike in 2010, their union said on Monday.

Controllers, who went on strike in June in response to sanctions handed down by AENA to 61 air controllers in Barcelona, will strike on July 11, 12, 25 and 26 for three hours each day.

The action will begin as Spain starts its summer tourism season and threatens to disrupt an industry that accounts for more than 10 percent of economic output.

AENA was not immediately available to comment. – Reuters