The ruling Union Solidarity and Development Party rejected calls to revise the 2008 Constitution.
"People will suffer bad consequences if the 2008 Constitution is abolished and redrawn," Thai newspaper The Irrawaddy quoted the party as saying Sunday.
The National League for Democracy, the main opposition group, said it was considering launching a campaign to review national laws.
The 2008 measure was written by the former junta. It allows for amendments but doesn't spell out how to draft a new document altogether. Opposition groups and ethnic parties in Myanmar say national reconciliation would be easier with new laws.
"There is no provision in the Constitution that allows us to have a new one," NLD spokesman Nyan Win told the Thai newspaper. "[This] could lead to a confrontation with the military."
NLD leader Aung San Suu Kyi took her seat in the Myanmar Parliament during by-elections last year. She said last week more women should be serving in the assembly.
Myanmar received praise for starting democratic reforms with general elections in 2010.