Kenko.com Inc., a unit of Internet retailer Rakuten Inc., said it has filed a lawsuit against the government to fight restrictions on the online sale of some drugs.

The government's ban is "unconstitutional," Kenko said in a statement to the Tokyo Stock Exchange on Tuesday. The suit was filed at the Tokyo District Court.

The filing came after Hiroshi Mikitani, the 48-year-old head of Rakuten, threatened legal action against the government and said he will step down from a key government council if Prime Minister Shinzo Abe pushed forward a bill that would prevent Internet sales of 28 drug products.

The Cabinet approved the bill for Diet action Tuesday.

The Kenko suit and online drug sales will be handled according to the law, said Chief Cabinet Secretary Yoshihide Suga. "It will be fought in the lawsuit," he said.

The possible resignation of Mikitani, one of Japan's leading entrepreneurs, would be a blow to Abe's image as he pushes legislation for his growth strategy. A Rakuten spokesman declined comment on Mikitani's possible resignation from the council.

The government has proposed restricting some online drug sales even after the Supreme Court in January allowed resumption of Internet sales.

The Japan Pharmaceutical Association, representing about 100,000 licensed pharmacists, had opposed online sales, saying they increase the risks that users will experience side-effects.

Kenko.com in January won a lawsuit seeking the government's withdrawal of a ban on selling over-the-counter drugs online. Kenko lost about ¥500 million in annual sales, or 30,000 orders, in 2009 when the government ordered it to stop sales of over-the-counter drugs, the company has said.