Although many airlines outsource the work to contractors, some airlines such as Aer Lingus and Ryanair provide baggage handling services for their passengers.
Workers in Madrid who handle checked luggage for Ryanair flights went on strike at the start of May in the dispute with the airline due to disagreements over workers' pay and conditions. Several unions took part in industrial action at first, altough only one, the CTA, is still on strike.
Ryanair would not confirm how many of the 200 luggage-handling staff it employs at Madrid airport are currently on strike, saying only that it is a "small number". The Dublin-based carrier claims that workers still striking are doing so illegally.
A spokeswoman for the company said: "The unions have failed to provide the legally required minimum service levels. We have lodged proceedings at the Madrid Labour Court against the one union which has not resumed full service, CTA... to prevent any such future disruption to our customers."
Passengers were asked to only travel with cabin baggage when the strike started due to the effects of the industrial action.
However, Ryanair says that its Madrid flights and baggage services are currently operating as normal.
When the strike started it was supported by some of the biggest unions in Spain: the CTA, UGT, CCCO and CGT.
They claimed that Ryanair was looking to cut workers' pay by up to 30pc.
A spokeswoman for the CTA added: "We had other problems such as the payment of bonuses during holidays, basic timetables for full-time workers [and] the respect for the remuneration of medical visits".
However, all unions except the CTA signed an agreement accepting the company's employment conditions on June 12.
The CTA has remained on strike and the spokeswoman claimed that Ryanair is looking to replace current staff with new low-paid workers "who do not know their rights". When asked about the claims made by the CTA union, a Ryanair spokesman said: "We don't comment on false claims made by unions, either here or in Spain."
There is no final judgment in the case yet. The case is due to be heard in the Madrid Labour Court in the coming weeks.
The strike is the second high-profile labour dispute Ryanair has had to grapple with in Europe recently.
Last week the company pulled its base in Copenhagen, moving its only aircraft based at the airport to Kaunas in Lithuania after a ruling by the Danish Labour Court that Copenhagen airport staff had the right to refuse to service its flights in a dispute over workers' rights.
The firm, headed by Michael O'Leary, left, had refused to enter into a collective bargaining agreement with a Danish union for pilots and cabin crew.
Read the original story at the Irish Independent.