The Ministry of Public Management, Home Affairs, Posts and Telecommunications on Tuesday urged Nippon Telegraph and Telephone Corp. to submit a voluntary business plan to boost competition among NTT group firms, a ministry official said.

Speaking to reporters earlier in the day, Toranosuke Katayama, minister in charge of telecommunications, said the plan should include steps to reduce NTT's equity stake in NTT DoCoMo Inc., its mobile phone arm, and NTT Communications Corp., its long-distance and international arm, to less than 50 percent.

NTT DoCoMo is currently owned 67.1 percent by NTT. NTT Communications is NTT's wholly owned company. NTT is owned 45.9 percent by the government.

The telecommunications giant is at odds with the ministry on this matter, on grounds that the company has to consider its shareholders' interests and that such a policy decision should be made independently by NTT management.

In the plan, the ministry also wants NTT to give total access to its regional telecommunications network and promote efficient operations at its two regional carriers -- NTT East Corp. and NTT West Corp.

At a regular news conference following the day's Cabinet meeting, Katayama said he thinks NTT will submit a plan covering all the steps requested by the ministry.

"If the plan is unsatisfactory, there could be a fundamental revision in line with the three-year deregulation plan (adopted by the government in March)," he said. The ministry was referring to the possibility of dismantling NTT as a holding company.

Katayama did not specify a deadline for NTT to submit the business plan, saying, "We must give them time, since boosting efficiency requires negotiations with the labor union."