Pilots’ unions have hailed a European Court of Justice (ECJ) ruling granting Ryanair workers’ the right to bring claims against the airline anywhere in Europe, but Ryanair insists not “one cent” will change.

The European Cockpit Association (ECA) signalled unions would challenge Ryanair in courts around Europe following the ECJ ruling on a case brought by six employees in Belgium in 2011.

The Belgian labour court went to the ECJ to establish whether it had jurisdiction and the ECJ ruled on Thursday that it did.

Analysts forecast the judgment against Ryanair and its temporary staff agency Crewlink could cost the airline €100 million, saying it undermined Ryanair’s claim that its crew are employed under Irish law and subject to that jurisdiction.

However, in a statement Ryanair insisted: “Ryanair will continue to employ its crew on Irish contracts.”

Ryanair chief executive Michael O’Leary conceded the ruling would give unions more scope to take the airline to court or “challenge whatever kind of provisions we provide in Ireland”.

But he said: “Ultimately, they cannot and will not be changing the Irish contracts or the structure of the Irish contracts. This won’t change Ryanair’s cost base by one cent.”

In its judgment, the ECJ noted the rules concerning jurisdiction in employment contract disputes are aimed at protecting the weaker party.

It found that contract clauses seeking to prevent employees from bringing proceedings in certain courts were not enforceable.

ECA leaders welcomed the ruling, saying: “The decision brings a definitive end to Ryanair’s fiction of considering a Ryanair plane as Irish territory, with Irish employees, subject to Irish jurisdiction.

“This claim has incorrectly designated Irish courts having jurisdiction over thousands of pilots and cabin crew and deprived many from access to legal help at the place where they actually work.

“The Court states the ‘home base’ of crews is the most ‘significant indicator’ to determine the employee’s habitual place of work and which laws and jurisdiction apply.”

The Irish Airline Pilots Association also welcomed the ruling.

ECA secretary general Philip von Schöppenthau said: “This Court ruling has repercussions well beyond Ryanair.

“Many airlines make use of highly questionable employment set-ups and doubtful contractual jurisdiction clauses.

“This EU-wide ruling makes it possible to challenge such set-ups. It will help plug the legal loopholes that allowed too many airlines to get away with practices that need to be examined and challenged by the courts.”

However, Ryanair signalled it would contest challenges under the ruling.

It insisted: “This ECJ decision does not change the status quo of Irish contracts of employment for Ryanair crew based across Europe.”

Instead, Ryanair hailed the ruling as “upholding its position by rejecting the argument that the home base (i.e where crew start and end their work day) should be the sole determinant of what court jurisdiction can hear disputes on labour issues”.

The airline argued: “The ECJ ruled that all factors such as where the worker gets their instructions, where goods/passengers are loaded/unloaded, where work tools are stored, where work is organised/performed and where the worker returns to at the end of their duty should be considered in conjunction with the home base in determining jurisdiction.

“This decision only updates the criteria for assessing the jurisdiction of national courts to hear legal cases locally and does not alter the law applicable to the contract.”

Ryanair chief people officer Eddie Wilson said: “We do not believe this will in any way alter our Irish contracts of employment.”