In Japan, every marriage costs one surname. The Supreme Court may change that on Wednesday.

A Civil Code that dates from the 19th century says couples must adopt one surname, and women almost always sacrifice theirs.

Five plaintiffs filed a lawsuit in 2011 saying the law was unconstitutional, violates their civil rights and puts the burden almost entirely on women. Two lower courts have ruled against them, setting the stage for Wednesday's Supreme Court ruling.

Supporters hope that the government's "womenomics" push to promote career advancement for women will somehow help their cause, though they are not directly related.

Here is a look at issue:

THE DEBATE: A growing number of women and their supporters started calling for change in the 1990s, prompting a Justice Ministry panel in 1996 to propose an amendment to allow separate surnames. The proposal was blocked by the ruling Liberal Democratic Party and conservatives who support traditional gender roles and family values centered on the oldest son. Opponents say allowing two surnames would destroy the sense of family unity. Supporters say the law must be changed to accommodate today's diverse family values and roles.

CIVIL CODE: Article 750 in the 1896 code says "A husband and wife shall adopt the surname of the husband or wife in accordance with that which is decided at the time of marriage." Although the law does not specify which name, 96 percent of women adopt their husband's surname. Many juggle two names, continuing to use their maiden name at work and the registered surname in legal documents. In Japanese tradition, a woman marries into her husband's household. However the surname of an only child often gets priority to preserve the family name.

AN OPTION: In order to keep their surnames, some couples choose not to register their marriages. Common-law marriages, however, can lead to complications in inheritance and parental rights. Only the spouse under whose surname the child is registered can have parental rights. Common-law spouses also are not heirs to their partners when there is no will, and cannot be a guarantor in case of a major medical operation or treatment.

PUBLIC DIVIDE: Recent media polls show slightly more than 50 percent supporting the right to keep separate surnames, while nearly 40 percent say Japan should stick to a unified surname. Support for a change is higher among younger people and women. If given the option, more than 70 percent said they would still adopt one family name.

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