Pilots at Ryanair's Stansted base have rejected an offer of significant pay rises by management.
They are the second group of employees to reject the pay offer, which was conditional on continuing to negotiate with the company through its 87 individual base Employee Representative Committees, rather than through unions, or through a new joint internal body known as the European Employee Representative Committee.
It is understood that contractor pilots who are not directly employed by Ryanair were not permitted to take part in the ballot.
However, there was a 91.2% turnout among direct employees, of whom 61% voted no.
Ryanair had warned that if the offer were rejected, pilots ran the risk of receiving no further pay rises for up to five years.
Stansted is one of Ryanair's biggest bases and the vote would seem to set pilots on a collision course with management over pay and conditions.
Pilots' key demands include collective negotiating rights and more permanent contracts, but Ryanair Chief Executive Michael O'Leary has consistently stated that he will only negotiate through local ERCs - a system that was validated by the Irish Supreme Court in a landmark case in 2008.
Pilots at Madrid have already rejected the offer made to their base.
Commenting on the ballot outcome, Ryanair said it was surprised that pilots had rejected large pay rises of up to £22,000 for captains and £11,000 for first officers.
It said the outcome vindicated how effective and democratic its internal collective bargaining processes are.
Ryanair said ten other bases have already agreed large pay rises.
It said it will continue to engage with pilots.
Meanwhile, the first Ryanair pilot to openly criticise management in the current crisis - Captain Imelda Comer - has urged pilots to stand together and demand better working conditions.
In a letter to colleagues, Capt Comer noted that up to half of the Stansted pilots were excluded from the ballot because they were contractors rather than being directly employed by the airline.
She queried who had made that decision, which "...clearly did not serve the best interests of the whole pilot body".
She noted that a 2015 survey had revealed that only 35% of pilots were direct employees.
She said that even if that percentage might have changed over the last two years, contractors still accounted for around half the pilot population - yet were completely excluded from any form of negotiations on decisions that fundamentally affected them.
Capt Comer told her colleagues that the Stansted pilots had rejected a management imposed solution to a problem that management had failed to understand - and that management had lost credibility in the eyes of the pilot body.
She alleged that management failures and misplaced actions could put the stability of their operations, and the sustainability of the company under further threat.
She described the current situation as "the ultimate farce in industrial relations, Ryanair style" adding that if the aim was to retain pilots, or attract new ones, it would fail.
Capt Comer concluded by saying: "It is time for the Ryanair board and its investors to question if the management team that got us into this mess are capable of getting us out of it."