Spanish national rail operator Renfe has canceled hundreds of trains on one of the busiest travel days of the year due to a strike over staffing levels.

The company said more than 700 scheduled services wouldn't operate Wednesday, a day when many people were heading off on their summer vacation.

The Spanish General Workers' Federation also plans walkouts on three other heavy vacation traffic days — Aug. 14 and 31, and Sept. 1.

The walkouts are held in two periods of four hours each. The government stipulated that a minimum number of services must run on each day of the strikes.

The workers' federation argues that a shortage of staff is leading to overwork and lower service quality. It says some 14,000 people work for state-owned Renfe.