Trade union Verdi has called on thousands of workers at German airline Lufthansa to go on strike on Monday to increase pressure on management in pay negotiations.

Verdi, representing about 33,000 employees, described a pay offer put forward by Lufthansa management on Wednesday as "scandalous" and said that it would represent a drop in pay in real terms over the next 12 months.

Staff held a one-day strike on March 21, forcing Lufthansa to cancel nearly 40 percent of its flights for the day.

Lufthansa's offer was to raise salaries by 1.2 percent from October this year and a further 0.5 percent a year later, in a deal that would run for 29 months and would not contain job guarantees.

Like European peers Air France-KLM and SAS, Lufthansa is trying to keep down staff costs as it battles competition from low-cost carriers and fast-growing rivals from the Gulf.

Verdi is demanding a 5.2 percent pay rise for cabin crew and ground staff at Lufthansa Cargo, Lufthansa Technik, Lufthansa Systems, catering unit LSG Sky Chefs and ground crews. It also wants a commitment by Lufthansa to safeguard jobs.

Friday's call for industrial action was for full-day strikes at Frankfurt, Europe's third-largest airport, as well as Munich, Hamburg, Stuttgart, Hanover, Duesseldorf, Cologne and Norderstedt.

Workers have been asked to strike during the morning in Nuremberg and until 8.30 ET in Berlin.

Lufthansa said it was too early to predict the exact impact on Monday's flight schedule but said that there would be delays and cancellations.

"We will, of course, put the necessary measures into place," a spokesman said just after the strike was announced.

The two sides have already agreed on April 29-30 and June 2-3 as dates for further pay talks.

Lufthansa shares were down 0.5 percent at 13.91 euros at 03.38 ET, underperforming a 0.4 percent rise in the Dax.

(Reporting by Victoria Bryan and Frank Siebelt; Editing by Christoph Steitz and David Goodman)