The party in Burma led by pro-democracy leader Aung San Suu Kyi will not attend tomorrow's re-opening of parliament because of a row over the oath of office for MPs.
Suu Kyi was among 43 MPs elected from her National League for Democracy party in by-elections in April.
They want to swear to "respect", rather than "safeguard" the constitution, which they say is undemocratic.
The constitution was drawn up by Burma's former military rulers.
A similar change in wording had to be made to the political registration law in order for the NLD to be able to take part in the latest by-elections.