A trade union representing flight attendants at KLM Royal Dutch Airlines threatened strikes over labour conditions on June 1.

Leen van der List, negotiator for the FNV Bondgenoten trade union, said KLM, the Dutch arm of Air France-KLM and unions were at odds over easing the workload of flight attendants.

Over the past years, labour agreements to improve efficiency and changes to KLM's European flight schedule have increased the workload of cabin staff and stretched their working hours, Van der List said.

He said the union's members had the last word and would decide the course of action by June 21.

"But we do want to send KLM the signal: if you don't do anything, you should expect industrial action," he said.

VNC, the second union representing cabin personnel, said it would submit KLM's offer to its members next week, also with a negative recommendation, and did not rule out strikes should KLM not move.

Van der List noted KLM's offer on pay rises -- 6.5 percent over two years -- was sufficient and above the average increases that had recently been agreed in the Netherlands.

The labour agreement for cabin personnel covers some 8,500 KLM employees. The FNV said that there was an agreement in principle for KLM's ground crews, who would get 6.5 percent wage increases over two years in an agreement running until the end of March 2009.

"We won't negotiate via the media," a KLM spokesman said.

"We have made an offer. We know of a number of parties that they will accept it, others first have to discuss it with their members," he said.