U.S. gender equality experts on Wednesday criticized a ruling by Japan's Supreme Court upholding a law requiring spouses to use the same surname, describing the law as outdated.

"Having the same name as her husband is not necessarily against her self-interest, but it should be up to her to choose," said Marsha Freeman, senior fellow and director of the International Women's Rights Action Watch.

"For many, it is a matter of having begun to establish a business or professional identity prior to marriage; changing it is detrimental to her professional life and well as to personal identity," she said.

On Wednesday, the Supreme Court ruled that a provision of the Civil Code requiring married couples to have the same surname is constitutional, noting that using one surname for family members is a practice "well-established in society."

In Japan, it is customary for a wife to take her husband's surname, although the law does not say which of the partners must give up their surname on marriage.

Freeman said the court is mistaken in its conclusion that a woman's use of their preferred name in all circumstances is a challenge to culture.

"Culture is a living thing that changes with time and the influence of information, education, and economics," she said.

Antonia Kirkland, legal adviser of Equality Now, a group working for the protection and promotion of women's rights, said the ruling symbolized gender inequality in Japan, adding men were often seen as more powerful in the country's traditional culture, leading many wives to give up their maiden names.

CNN reported the ruling, saying that many women, gender equality experts, and even a U.N. committee have said the law was "discriminatory" and "outdated," with its headline reading "Japanese women lose fight to keep their surnames."