Ground staff at Berlin's two airports will start a 25-hour strike on Monday, the Verdi union said on Sunday, stepping up action in a pay dispute that has already caused the cancellation of around 1,000 flights.

Workers at Berlin's Tegel and Schoenefeld airports will walk out at 4 am local time (0300 GMT) on Monday and end the action on Tuesday morning at about 5 am local time (0400 GMT), said Verdi in a statement.

The union wants an increase in pay for ground staff to 12 euros ($12.80) an hour from about 11 euros as part of a one-year collective agreement. The employer is offering about 10 cents more an hour over four years.

Carriers including Air Berlin, Lufthansa, easyJet and Ryanair serve the two airports.

More at Reuters.