The part-time administrative position with Zurich-based food wholesaler Ernst Welti AG involves shifts staring at 9pm and might not seem the most appealing position for a mother with small children.
But for Corinne Schärer, a board member with Swiss union Unia, the advertisement for the position is simply "not on".
"The ad promotes the idea that having small children in the workplace is a problem," she told The Local on Friday.
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"It also shows a very conservative image of women and their place in the workforce for this day and age," she added.
Schärer stressed the job post was almost certainly discriminatory under the Federal Act on Gender Equality.
That legislation prohibits companies discriminating against employees on the basis of their sex or family situation. It means, for example, that candidates do not have to ask questions about their family life or whether they plan to have children during a job interview.
Meanwhile, the firm behind the ad explained to Swiss news site 20 Minuten that the wording had been chosen because mothers of young children tend to be absent more often because either they are ill or their children are sick.
Ernst Welti sales manager André Marquart said the night shift team was made up of just three people and that things were stressful if someone was absent.
"We have nothing against the mothers of young children," Marquart said.
"But they tend to stay home [if their child is sick], which is completely understandable."
For Schärer, though, the ad is further proof that Switzerland has a long way to go on gender equality in the workplace. She noted the relatively short maternity leave available to women – mothers are granted 14 weeks – and the fact that childcare is very expensive.