"The European Sunday Alliance is only at the beginning — we count on other groups and organizations joining the campaign as well," she said. "It's clear there's growing support for the kind of steps the alliance is recommending."

In a founding declaration, the alliance said decent working hours were of "paramount importance" to citizens of the European Union, which should uphold "the social contract of a modern European society" by encouraging "reconciliation of professional and family life."

"Only a well-protected, common work-free day enables citizens to enjoy full participation in cultural, sports, social and religious life, to seek cultural enrichment and spiritual well-being," said the declaration.

Calls for the preservation of work-free Sundays have increased in the EU, where shops and businesses now routinely require staff to turn up on weekends without extra pay.

In its declaration, the European Sunday Alliance said irregular hours were creating "unsustainable working time patterns" and having a "serious negative effect" on health and safety by fueling stress, illness and absenteeism. It added that they were also the main source of "working poor" in Europe and said the EU should "ensure its legislation and internal market rules better guarantee the work and life balance."

"People usually work on Sundays or at irregular hours out of financial necessity rather than choice," it said.