A pilot of German airline Lufthansa attaches a button reading "we are on strike" on his uniform as he takes part in a demonstration during a strike of the German airline Lufthansa pilots at Frankfurt airport, Germany, November 30, 2016. REUTERS/Kai Pfaffenbach - RTSTYZ0

FRANKFURT (Reuters) - Lufthansa LHAG.DE and pilots' union Vereinigung Cockpit (VC) will decide next week whether to accept a deal proposed by a mediator to settle a long-running labor dispute over issues including pay.

Mediator Gunter Pleuger, a former diplomat, presented his proposal behind closed doors on Friday, while Lufthansa and VC agreed to make a decision on Feb. 15 over whether or not to accept, a spokesman for the airline said.

Lufthansa’s pilots have walked out 15 times since early 2014 over disputes with management on topics including pay and early retirement, costing the carrier hundreds of millions of euros in lost profits.

Most recently, they were on strike for six days in November, costing the airline a further 100 million euros ($106 million) in profits.

Before the mediation process, the pilots had asked for an average annual pay increase of 3.7 percent over a five-year period back-dated to 2012, which is when their last collective bargaining contract with Lufthansa expired. The pilots say altogether these increases would amount to a rise of nearly 20 percent on current pay.

Lufthansa had proposed an increase of 4.4 percent in two installments in 2016 and 2017, plus a one-off payment worth 1.8 months’ pay.