A new law in Iceland requires companies to prove that their pay practices do not discriminate against women.
The law was passed with a large majority by the parliament in Reykjavik in June and took effect at the New Year.
It seeks to erase a persistent gap between men and women's pay despite years of equality legislation dating back to 1961.
Companies with more than 25 workers will have to obtain a certification from an accredited auditor that they are basing pay differences on legitimate factors such as education, skills and performance.
Big companies with more than 250 employees have until the end of the year to get the certification, while the smallest have until the end of 2021.