(Bloomberg) -- Lufthansa AG has billed a cabin-crew union for pay it says some staff received when they were actually working for the labor group, marking the latest in a series of spats with employee representatives.

The people were paid at various times between 2015 and 2018 when they were engaged with the UFO union rather than flying, Lufthansa said in a statement Friday, adding that it’s seeking reimbursement for the hours concerned.

Lufthansa said staff can be exempted from work to perform union duties, but must lodge applications for their salary to be split between it and the relevant labor group -- with no such submissions received for the period in question.

A spokesman for UFO said the move is an attempt to discredit it.

Relations between Lufthansa and a number of unions have deteriorated in recent years as it seeks to cut costs to sustain margins against a background of falling fares. The biggest bone of contention has been a plan to switch flights from the main brand to low-cost arm Eurowings, where pay is lower.

To contact the reporter on this story: William Wilkes in Frankfurt at wwilkes1@bloomberg.net

To contact the editors responsible for this story: Reed Landberg at landberg@bloomberg.net, ;Anthony Palazzo at apalazzo@bloomberg.net, Christopher Jasper, Andrew Noël

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