The Diet passed a bill Wednesday to fine companies for giving false information in their financial statements and to tighten rules on large-lot off-hours stock trading.
The Securities and Exchange Law revisions were approved by the Upper House.
The penalties for false information will take effect in December and the off-hours trading amendments will go into force in July.
The legal changes come on the heels of a string of scandals involving the falsification of financial information by firms that include Seibu Railway Co. and Kanebo Ltd.
The off-hours changes follow Internet service provider Livedoor Co.'s surprise acquisition of a massive number of Nippon Broadcasting System Inc. shares outside the exchange's normal trading hours in early February.
Under the revised law, a firm that has provided false financial statements will be fined either 3 million yen or 0.003 percent of its total market capitalization, whichever is higher.
If a company issued false statements over a number of years, the fine will have to be paid for up to three years.
The law will also expand the current open tender regulations to cover large-lot off-hours stock deals when buyers seek to acquire more than one-third of a company.
At present, the open tender regulations oblige large-lot equity buyers in off-market trading to publicly announce a price, a tender period and other details of a massive share acquisition. But they do not cover large-lot equity purchases during off-hours trading.