Almost half the members of Vietnam's National Assembly have failed to support a proposal from the Prime Minister on his first day in office.
The new prime minister has promised to tackle corruption
Assembly members were angry at a decision to allow the transport minister to retire without punishment.
Many felt he should take responsibility for a multi-million dollar corruption scandal in his ministry.
The Assembly has been a rubber stamp for the Communist Party, but is showing signs of independent thinking.
In the vote, 44% of its members either abstained or voted to reject a proposal by the new Prime Minister, Nguyen Tan Dung, to allow Transport Minister Dao Dinh Binh to retire along with his colleagues.
Nguyen Tan Dung, 56, Prime Minister
Groomed for top by outgoing PM Phan Van Khai
Army background suggests politically conservative
Southerner thought to favour more economic reform
Nguyen Minh Triet, 63, President
Party chief in Ho Chi Minh City, reputed to favour economic openness
Was in charge when underworld figure Nam Cam tried and executed
Two weeks ago, in live televised question and answer sessions, members angrily accused Mr Binh of failing to stop the country's biggest corruption scandal.
Millions of dollars, some of it overseas aid, was skimmed off official road-building contracts and gambled on European football matches.
Mr Binh resigned and escaped punishment but many members wanted to make an example of him.
They failed and the Prime Minister won the vote - but such a significant show of dissent is unusual in Vietnamese politics.
It also marks an uncertain beginning for the prime minister's term of office.
He has promised to root out official corruption but has begun by letting one accused minister off the hook.