Garbage piled up at Madrid's Barajas airport, one of Europe's busiest, on Monday due to a strike by cleaning staff over salary cuts and job losses.

Papers, empty plastic bottles and drinks cans littered the floor of the airport, Europe's fourth-busiest by passenger numbers, with 45 million passengers last year.

Workers of the Pilsa cleaning firm, which is responsible for keeping three of the airport's four terminals clean, have been on an open-ended strike since January 24 to protest against the elimination of 54 jobs.

Cleaning staff belonging to the Eulen cleaning company, a unit of Spanish services firm Alentis, which cleans Terminal 4, joined the strike on Sunday night to protest its decision to cut their monthly salary by 400 euros ($540), a 30-percent reduction.

They are also protesting against the elimination of certain benefits, such as the payment of a bonus for working on a public holiday.

Union and company officials were due to meet on Monday to seek a settlement to stop the strike.

"Negotiations remain open. We are in constant contact with workers' representatives and are confident that we can find a favourable solution for everyone," said Alentis spokesman Joaquim Alvarez.