Additional paid sick days for women with severe menstrual problems - the left-wing Spanish government passed such a regulation on Tuesday.
Should the regulation also be approved by Parliament, it would be a first in Europe.
But the reform is controversial even among trade unions and those affected.
Some of them warn that because of the special arrangement, employers may fear that women will be absent from work more often - and therefore give preference to men when hiring.
Extra sick days for women with severe menstrual problems are only available in a few countries outside of Europe, including South Korea and Indonesia.
The government of Spain's socialist Prime Minister Pedro Sánchez has passed the regulation as part of a reform of the abortion law.
"The period will no longer be taboo," said Equal Opportunities Minister Irene Montero from the left-wing Podemos party in a press conference after the cabinet decision.
Spain will be "the first country in Europe" with fully state-funded sick days for severe menstrual cramps.
Those affected should take as many sick days as they need.
As with other sick leave notifications, a medical certificate is required.
Spanish media initially reported that up to five additional sick days were granted each month.
However, it may be months before a parliamentary decision on the reform is made.
In addition, it is uncertain whether Sánchez's minority government, which has made strengthening women's rights one of its priorities, will receive enough support for the reform in parliament.
"No more going to work in pain, no more taking pills before arriving at work and having to hide the fact that some days we are in so much pain that we are unable to work," Montero campaigned for her law on Tuesday.
However, this is also controversial within the government alliance.
Some socialist cabinet members fear that the supposed preference given by additional sick days will put women at a disadvantage when looking for a job.
For fear that women could be absent particularly often, companies would then prefer to hire men.
The reform is also controversial among employee representatives.
"You have to be careful with this type of decision," warned Cristina Antoñanzas, vice-president of the UGT, one of the two largest trade unions in the country.
Sick days for menstrual problems could have an indirect impact on “women’s access to the labor market”.
The association of victims of endometriosis, a chronic gynecological disease that is often associated with particularly painful menstrual bleeding, also has reservations.
"More than days off, we need an acknowledgment of our impairment," said association leader Ana Ferrer.
She fears "discrimination" against women because of their menstrual problems.
Spain's second largest trade union, the CCOO, sees the reform plans as a major "legislative advance" in "making visible and recognizing a hitherto ignored health problem".
Apart from the additional sick days, the reform package drawn up by the Ministry for Equal Opportunities provides for further simplifications for women.
For example, VAT on certain hygiene products for women, such as pads or tampons, is to be completely abolished.
In addition, abortions in state hospitals are to be made easier.
According to the reform project, young people should be allowed to have abortions from the age of 16 without parental consent.
In Catholic Spain, abortion has only been legal since 1985.
At that time, abortion was legalized after rape, in the event of fetus malformations or because of physical or psychological risks for the woman.
Since 2010, abortions up to the 14th week of pregnancy have been generally permitted.Keywords: