TOKYO — On paper, Japan has one of the best paternity leave policies in the world. In practice, very few men — less than one in 16 — take advantage of their legal right, often because they fear retribution.

Now two men in Japan who did take time off to care for newborns are suing their employers, saying the companies punished them with demotions and pay cuts after they returned from paternity leave.

Their lawsuits, which are highly unusual in Japan, are prompting a discussion in the country about longstanding cultural norms and company expectations. Overwhelmingly in Japan, women still assume responsibility for the vast majority of child care while men are expected to show extreme loyalty to their employers at the expense of their families.

The first hearing in one of the lawsuits took place in Tokyo District Court on Thursday, just a day after Japan’s new environment minister said he was considering taking paternity leave early next year.