The movement threatens to disrupt primarily the French-language production of Agence France-Presse during a period of major domestic news, with a ceremony for the 80th anniversary of the D-Day landings, EU elections and a TV appearance by President Emmanuel Macron.
Unions within AFP called for the strike after a post in Brussels was changed from a "headquarters" contract to a "local" contract, which carries less generous housing and social benefits.
The unions see this as part of a wider move to curb the number of headquarters-status posts in the agency, which operates in 150 countries.
"The staff demands the maintenance at the current level, i.e. 151 positions, of the network of expatriates with headquarters status in all languages," said a motion voted by staff on Monday.
In an internal note, management said it was committed to "maintaining a strong global network with a significant population of expatriate journalists".
"AFP alone among the global agencies has such an expansive programme and we believe strongly in its virtues," it added.
But it said increasing global taxes and social charges had made maintaining the expatriate network more expensive, adding that reform was necessary to make the system "fairer and more diverse".