Pilots on Lufthansa's long-haul fleet have started a 15-hour walkout at the airline's main Frankfurt hub in a festering contract dispute.

The Vereinigung Cockpit union called members out on strike from 8 a.m. (0600 GMT) Tuesday in its fourth limited several-hour walkout over recent weeks and the first since a new round of talks collapsed last week.

Lufthansa said it plans to go ahead with 32 of the day's 57 scheduled intercontinental flights from Frankfurt — 26 flown by volunteer pilots, the other six pushed forward or back to Wednesday.

The two sides are at odds over the pilots' demand that Lufthansa keep a transition payment for those wanting early retirement.

The airline, facing competition from European budget airlines and major Gulf carriers, wants to cut those payments.