YANGON (Reuters) - Myanmar's military has jailed an officer for two years for signing a petition supporting a constitutional amendment to reduce the army's role in politics, the officer's wife said Monday.

The National League for Democracy (NLD), led by Nobel laureate Aung San Suu Kyi, spearheaded a campaign earlier this year to rescind Section 436 of the constitution, which gives unelected military MPs veto power over further amendments to sections, including one that bars Suu Kyi from the presidency.

Over the past year, Suu Kyi, whom the former junta kept under house arrest for years, has been critical of the government, accusing it of stalling on reforms.

A military tribunal on Friday convicted Major Kyaw Zwar Win after arresting him in April, said his wife who asked not to be identified by name. "He wasn't granted the right of defence through lawyers during the trial in accordance with the practice of court martial," she told Reuters. "He was sentenced to two years in jail for disobedience."

The military has no spokesman and does not speak to journalists. The office of government spokesman Ye Htut did not answer calls requesting comment.

Myanmar's former ruling junta, which repeatedly cracked down on pro-democracy protests, stepped aside in March 2011. A semi-civilian government has since introduced reforms, including the release of political prisoners.

While the military ceded nominal political power to civilians, including former officers who retired to join the USDP, it cemented its role in government through the constitution it drafted in 2008.

Major changes must be supported by more than 75 percent of parliament, which allows military MPs and their USDP allies to veto any proposed amendments.

During the NLD's petition drive, the military issued orders that no officers should add their signatures, according to Nay Myo Zin, a former military officer who is now a political activist.

Under the constitution, 25 percent of the seats in parliament are set aside for the military. And more than half of the rest are held by the Union Solidarity and Development Party (USDP), made up mainly of former officers.

The NLD and political activists collected about five million signatures on their petition for constitutional change, which they presented to parliament in August.

Aung Thein, a legal adviser to the NLD, said his team would provide assistance should Kyaw Zwar Win wish to appeal the verdict, but his wife said he had no plans to appeal.