Deutsche Lufthansa’s pilots are set to extend strikes into this week after the latest round of labour talks failed, making the current conflict the longest protest by cockpit crews at the German airline.

Pilots at the mainline Lufthansa brand will strike on short-haul services on Tuesday and expand the protest to also include intercontinental flights on Wednesday, the Vereinigung Cockpit union said. Including four days of strikes last week, the work stoppage is set to be the longest in the company’s history, surpassing a four-day walkout in March 2015.

Lufthansa risked further escalating tensions by seeking to have the latest strike blocked by the Munich Labor Court. A judge will now look into the filing and then decide how to proceed, a court spokesperson said Monday by phone. A spokesperson at Vereinigung Cockpit declined immediately to comment on the airline’s effort. Lufthansa spokesperson Helmut Tolksdorf said the company didn’t plan other legal action outside the Munich filing.

The current protest has so far led to about 2,800 flight cancellations, disrupting travel for around 350,000 people. If the strike continues as planned, it may cost the airline about 45 million euros (approximately $64 million), based on estimates from the company.

A long-running spat over wages, working conditions and the role of discount unit Eurowings within the group intensified last week after chief executive officer Carsten Spohr sought to block what started as a single-day walkout. When a Frankfurt labour court dismissed the case and an appeal failed, Vereinigung Cockpit retaliated by extending the protest. The CEO has refused to cave in to wage demands as he seeks to trim costs to weather intensifying competition from budget rivals such as Ryanair Holdings Plc.

Vereinigung Cockpit is seeking a 20-per-cent raise for its members spanning the period from 2012, when the last accord expired, through 2017, equivalent to 3.7 per cent a year. Lufthansa has offered 2.5 per cent for a six-year period and last week reiterated its willingness to lift that to 4.4 per cent plus a bonus payment, provided the pilots agree to concessions in retirement benefits, seniority bonuses and other perks.

“There still is no negotiable offer from Lufthansa, so the industrial action must continue,” union spokesperson Joerg Handwerg said in a release after a Sunday meeting with management.

Adding fuel to the fire, Spohr responded to the extended strikes last week by reviving a two-year-old legal case seeking 60 million euros (about $85 million) in damages from the union related to an earlier walkout. Vereinigung Cockpit called the move an attempt to destroy it.

Lufthansa has said the protests cause about 10 million euros (about $14 million) in damages on days when both European and long-haul flights are affected. The airline has had to book 4,000 hotel rooms for stranded passengers and set up 400 camp beds at its Frankfurt hub for people due to catch connecting flights. Meanwhile, with Christmas just four weeks away, extended protests could hurt forward bookings into the busy holiday season.