FRANKFURT (Reuters) - Lufthansa (>> Deutsche Lufthansa AG) pilots threatened further strike action on Tuesday as they began a 15 hour walkout at Frankfurt airport in a row with management over retirement benefits that stretches back two years.

The pilots, represented by union Vereinigung Cockpit (VC), are striking from 0600 (7 a.m. BST) to 2100 GMT (10 p.m. BST) on long-haul routes from Frankfurt, Europe's third-largest airport and Lufthansa's main hub.

The strike, affecting around 9,000 travellers, is the longest since a three-day nationwide walkout in April, and the union threatened more.

Three strikes since the end of August have targeted specific operations such as those at Munich or Frankfurt and budget unit Germanwings and have lasted around six to eight hours.

"We're not on the same level for talks," VC board member Markus Wahl told Reuters on Tuesday. "If Lufthansa doesn't make a move, then further strikes will happen."

The pilots are trying to increase pressure on management to maintain a retirement scheme that gives pilots the option to retire from the age of 55 and still receive up to 60 percent of their pay until regular retirement.

Lufthansa, in the midst of a cost-cutting plan and trying to set up new low-cost units to battle tough competition, wishes to alter the scheme for new pilots, so that the average age at which its pilots retire rises to around 60.

Lufthansa, Europe's largest airline by revenue, has cancelled 25 of 57 long-haul flights planned for Tuesday as a result of the strike. In total, around 50 flights have been cancelled from Monday to Wednesday in order to ensure crews and planes are not stranded.

As in previous strikes, the airline is using managers with pilots' licences to keep planes flying. "We've managed to keep one in every two flights in the air," a spokeswoman said.

Lufthansa is not the only flag-carrying airline in Europe struggling with labour relations. Air France (>> AIR FRANCE-KLM) pilots called an end to a two-week strike over the weekend in a row over low-cost expansion.

(Reporting by Peter Maushagen; Writing by Victoria Bryan; Editing by Elaine Hardcastle)

Stocks treated in this article : AIR FRANCE-KLM, Deutsche Lufthansa AG
Valeurs citées dans l'article : AIR FRANCE-KLM, Deutsche Lufthansa AG