* Union calls for warning strike ahead of talks on Friday
* Strike likely to last from 0400 GMT to 0900 GMT
* Frankfurt and Hamburg airports to be most affected
* Shares down 0.2 percent
By Maria Sheahan
FRANKFURT, March 20 (Reuters) - Deutsche Lufthansa has cancelled more than 500 flights after German union Verdi called on 33,000 workers at the company to go on strike on Thursday over a wage dispute.
The strike is expected to last for about five hours from 5am (0400 GMT), the union said on Wednesday, setting the stage for the next round of wage talks on Friday.
Efforts by big European airlines such as Lufthansa and Air France-KLM to shrink costs in the face of soaring jet fuel prices and fierce competition from Middle Eastern airlines and low-cost carriers have fanned tensions with workers.
Strikes at Spanish airline Iberia, for instance, caused thousands of flight cancellations at a cost of about 30 million euros ($38.7 million) until workers accepted a mediated deal last week.
In negotiations that started last month, Germany's Verdi is demanding a 5.2 percent increase in wages for 12 months for employees at Lufthansa Cargo, Lufthansa Technik, Lufthansa Systems, catering unit LSG Sky Chefs and ground crews, as well as a commitment by Lufthansa to safeguard jobs.
Lufthansa, Europe's biggest airline by revenue, has said it wants to freeze pay and ask employees to work one hour more each week to help it to remain competitive in a tough market. Verdi called that counter-demand a "provocation" and called on Lufthansa to make a new offer.
Thursday's strike will affect operations across Germany, though Hamburg and the airline's main hub in Frankfurt will be most affected, the union said.
A list posted on the airline's website on Wednesday afternoon showed a total of 514 cancelled flights, mostly to German and European destinations. Lufthansa said it aims to get most intercontinental flights off the ground despite the strike.
Travellers in Germany have already suffered this year as repeated strikes by airport security staff caused cancellations and delays.
Strikes, capacity cuts by airlines and harsh winter weather led to a 3.6 percent decline in passenger numbers at German airports in January and February, the worst start to the year since 2009, airports group ADV said on Wednesday.
Shares in Lufthansa were down 0.4 percent at 16.24 euros by 1442 GMT, while Germany's blue-chip DAX index was up 0.5 percent.