Dozens of flights have been cancelled after security personnel walked off the job at Germany's Cologne airport in a wage dispute.

Verdi union spokesman Ozay Tarim said on Friday that some 150 security personnel started their one-day warning strike at 4am. German police stepped in to take over security checks but some 50 flights were still canceled due to the strike.

Airport workers in recent months have staged several such daylong "warning strikes", which are often used to increase pressure in German wage negotiations. It's the fourth strike in Cologne since the start of the year and airports in Duesseldorf and Hamburg have also been targeted.

The union seeks a roughly 30% increase for the private security workers. Employers have offered a 9% raise.