The strike by apron controllers at Europe's third-busiest airport in terms of passenger numbers, which grounded hundreds of flights last week, went into a third day on Monday and was scheduled to continue until 0400 GMT on Wednesday.

A spokesman for the GdF union said it was quite likely that the workers would strike again on Wednesday.

The walkouts started last week after GdF and airport operator Fraport (FRAG.DE) failed to reach an agreement on wages for about 200 workers who guide planes in and out of their parking positions.

Fraport said 231 flights, of a total 1,250 scheduled for Monday, would be cancelled, with a similar number to follow on Tuesday.

Lufthansa (LHAG.DE), which accounts for more than half of flights at Frankfurt airport, said it expects to cancel about 200 incoming and outgoing flights on German and European routes on Monday, while all intercontinental flights would take place.

The situation will not be as bad on Tuesday, with only around 160 flights cancelled, Lufthansa said. A further eight flights on Wednesday were also cancelled, according to its website.

Air Berlin (AB1.DE), Germany's second-biggest airline, showed a total of eight cancelled flights between Berlin and Frankfurt on Monday and Tuesday.

The apron controllers, who represent about 1 percent of Fraport's staff at the airport, want higher pay, arguing their jobs have become more complex since the fourth runway started operating last October.

Fraport has said demands for pay increases of between 50 and 70 percent are unreasonable, and has called on the union to resume talks.

However, neither side has shown any signs of backing down. The union says it could strike for weeks yet, while Fraport has said it can continue to use other operations management staff.

Fraport estimates that two days of walkouts last week cost it 3.5-4.0 million euros in lost revenues. Analysts estimate that Lufthansa may have lost 40 million euros in revenues during that time.

Silvia Quandt analyst Stefan Kick said Fraport was making the right move by holding out, even at the risk of a protracted battle, rather than giving in to workers' demands.

"If Fraport agreed to the wage increases the company would run the risk that other small but important employee groups also ask for massive wage increases," he said.

The GdF, which also represented air traffic controllers in a bitter wage dispute last year, must give 24 hours' notice of any further strikes.

(Reporting by Maria Sheahan and Peter Maushagen; Editing by Greg Mahlich and Erica Billingham)

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