The International Transport Workers' Federation (ITF) is running a campaign against Qatar Airways over its monitoring of staff and rules preventing women from becoming pregnant and getting married.
It has called on women across the globe to speak out against the airline on Saturday, International Women's Day.
"The treatment of workers at Qatar Airways goes further than cultural differences. They are the worst for women's rights among airlines," Gabriel Mocho, civil aviation secretary at the international grouping of transport unions, told Reuters.
A Swedish newspaper last year published a report entitled "The truth about the luxury of Qatar Airways," which described restrictions imposed on cabin crew.
At the ITB travel fair in Berlin, Qatar Airways Chief Executive Akbar al Baker reacted furiously to questions about the article and said people were attacking Qatar because it had won the right to host the 2022 soccer World Cup.
Qatar has been criticised for its treatment of migrant workers helping build facilities for the World Cup.