The Diet enacted a legal revision Friday aimed at lowering mobile phone fees and spurring competition in the country's saturated telecom market.

Amid criticism that Japanese carriers charge too much compared with other countries, the bill to amend the telecommunications business law, passed by the House of Councillors, bans them from offering plans that cover both the price of a mobile phone and connection fees in one package.

For many years, Japanese carriers have discounted mobile device purchases in exchange for relatively high data usage fees.

Consumers and government officials have said the plans make it difficult to compare the fees charged by carriers.

The issue came into the spotlight in August last year when Chief Cabinet Secretary Yoshihide Suga said the three major carriers -- NTT Docomo Inc, SoftBank Corp and KDDI Corp -- could reduce their fees by around 40 percent.

The three carriers control nearly 90 percent of the domestic mobile phone market.

The new law will take effect as early as this fall after the Ministry of Internal Affairs and Communications compiles guidelines for fee plans.

NTT Docomo unveiled a new plan in April that will cut mobile phone charges by up to 40 percent and also offered to separate handsets and service charges.