More than 200,000 passengers could be affected by the strike

Dutch unions said Wednesday they have called for a strike by security staff next month at Amsterdam's Schiphol airport, one of the world's busiest.

More than 200,000 passengers could be affected by the September 4 strike, according to Dutch press agency ANP.

The announcement follows nearly two months of action by security staff in various parts of to country to push for better working conditions.

Security staff at Schiphol are seeking a three percent salary hike, more flexible working hours and increased security.

"Employers have so far refused to meet these demands," unions said in a statement.

Schiphol airport said it would appeal to companies and to try to reach an agreement before September 4.