The labor ministry has decided to make it unlawful to demote, reassign or otherwise treat female employees unfavorably during a yearlong period following their return from child-care leave, ministry officials said. If a company insists circumstances necessitate such treatment, it will be obliged to explain why, the officials said. Firms can currently force women to accept such treatment without due cause — so-called maternity harassment — merely by citing reasons such as the individual’s lack of ability. Last October, the Supreme Court ruled that demotion due to pregnancy is prohibited in principle by law and is unlawful unless women accept it without compulsion or there are special circumstances necessitating it. On the basis of the landmark decision, the Health, Labor and Welfare Ministry has distributed new guidelines to labor bureaus across the country.