French women workers are paid on average 15.5 percent less than their male counterparts, Rebecca Amsellem of the Glorieuses newsletter has calculated.
That means that they are effectively not being paid for the work they do between Monday afternoon and 1 January 2017, she points out on the Thunderclap website.
Although another women's rights group, Les efFronté-e-s, called a rally on Paris's Place de la République at the fatal hour, Amsellem did not call for strike action, as some coverage in the French media might have led one to believe, simply calling for the question to be taken up politically.
France higher than EU average
On 24 October women in Iceland, where women are paid on average 14 percent less than men
, did walk off the job to join a massive demonstration to call for equal pay.
The gender pay gap is actually lower in France than many other countries, most notably South Korea where women were paid 36.6 percent less than men in 2010.
France is 14 out of 28 in the equal-pay stakes in the European Union, with Austria, Germany, Slovakia, the Czech Republic and Hungary the worst offenders and the UK and Finland not far behind.
Pay discrimination against the law
French law actually forbids employers from discriminating against workers on the grounds of sex, as for a number of other factors including physical appearance, race, physical disability, sexual orientation, political opinions or private life.
So women workers who can prove they are being paid less than a male colleague for the same work can take their employer to court.
But the pay gap still exists for a number of reasons, detailed by researchers:
Women's work is undervalued: Jobs requiring similar skills, qualifications or experience tend to be poorly paid if they are mainly done by women, for example supermarket cashiers usually earn less than other more physical tasks;
Segregation in the labour market: Women often work in sectors, such as health, services and public administration, that are lower-paid than those where men are more highly represented - 88 percent of French women workers are in services, compared to 64 percent of men and their pay is 27.5 percent lower than their male counterparts;
Work and family: Despite increases in paternity and carers' leave, women tend to look after dependent family members, for example 65.8 percent of women with young children in the EU work, compared to 89.1 percent of men, and in France women devote an average of 3.5 hours a day to domestic tasks, compared to two hours for men;
Part-time work: Family responsibilities and other choices or pressures mean that 32 percent of women work part-time across the EU (30.4 percent in France), compared to eight percent of men (seven percent in France), and 80 percent of French part-time workers are women;
Missed career opportunities: Pregnancy, maternity leave, domestic responsibilities and part-time work lead to an interruption of women's careers that often have a permanent effect on their pay and their chances of promotion;
Discrimination: Even if all those factors are taken into account, there is a gap of nine percent between French men and women with the same qualifications, doing the same job, the result of "pure discrimination practised by employers", according to the Observatoire des inégalités NGO.
To read our history of the fight for women's rights in France click here