(CNN) -- The Myanmar opposition leader Aung San Suu Kyi and members of her party are unlikely to attend the first session of parliament since their election amid a dispute over the wording of the oath that lawmakers have to take, a party spokesman said Friday.
Suu Kyi and 42 other candidates from her party, the National League for Democracy, won seats in by-elections on April 1, a result welcomed by countries like the United States and Britain as a sign of progress toward democracy in Myanmar after decades of repressive military rule.
Following the elections, Suu Kyi and other newly elected opposition members were invited to attend the session of parliament next week in the capital of Naypidaw.
But they have requested that the wording of an oath that lawmakers have to take be changed. The NLD asked the authorities to adjust the wording of the oath to say that parliamentarians will "abide by the law" rather than "protect the constitution."
In a letter to the NLD, the government didn't respond directly to the request, it said only that the parliament session next week would be a continuing session, so there would be no oath taking ceremony, said Nyan Win, a spokesman for the NLD.
That response failed to satisfy opposition officials and there is now a 90% chance that Suu Kyi and the other newly elected NLD members will not go to parliament on Monday, Nyan Win said.
The tension over the oath is the first sign of contention between the opposition and the reformist government of President Thein Sein. The situation is complicated by Thein Sein's being out of the country at the moment: he is visiting Japan until early next week.
Myanmar's authoritarian military rulers have begun loosening their grip on power after decades in which dissent was stifled and freedoms severely limited.
In the past 12 months, the government has pardoned hundreds of political prisoners, secured a cease-fire with Karen rebels and agreed to negotiate with other ethnic rebel groups.
U.S. Secretary of State Hillary Clinton described this month's by-elections as "an important step in Burma's democratic transformation."
Western governments have applauded the elections and the other recent reforms by the government of President Thein Sein. The U.S. and Australian governments eased some sanctions on Myanmar this week.
Clinton visited Myanmar in December, a historic trip marking the first time a secretary of state had been to the country in more than 50 years.
While control of parliament will not change despite the opposition's strong performance in the by-elections, the result nonetheless gives the National League for Democracy a notable presence.
Myanmar's legislature has 664 seats, more than 80% of which are still held by lawmakers aligned with the military-backed ruling party, the Union Solidarity and Development Party.
Suu Kyi led her party to a landslide victory the previous time Myanmar held multiparty elections, in 1990. But the junta ignored the results and kept her under house arrest.
Released in November 2010, Suu Kyi was allowed to crisscross the country to rally support for her party in the elections.
This week, it was announced that she would make her first overseas trip since her detention.
Suu Kyi will travel to Norway in June to deliver the speech she was unable to give when she was awarded the Nobel Peace Prize in 1991.
CNN's Jethro Mullen contributed to this report.