Alliance leader Laila Harre is criticising part of the local government bill on water management that she approved as a cabinet minister and which the Alliance supported.
The criticism could be seen as a breach of collective cabinet responsibility, a potentially sackable offence.
Prime Minister Helen Clark said shewould keep an eye on such comments during the election campaign.
"I'll have to think about the consequences of this sort of thing during the campaign ... We'll see if it becomes a habit."
But she said there were no votes imminent, and she did not believe Laila Harre would be in the next Parliament to vote on the legislation in question, the Local Government Amendment Bill.
In carefully chosen words, Laila Harre said the Alliance wanted to "strengthen the anti-water-privatisation provisions" of the bill.
One of the clauses allows for contracting out management of water services to the private sector.
"This is a form of privatisation that the Alliance will move to take out of the legislation at select committee," she said.
"While the bill makes progress towards the Alliance position, the contracting-out provision is a loophole that should be closed.
"This election gives us a chance to get a fresh mandate to oppose the direct and indirect privatisation of key infrastructure."
The bill is in the name of retiring Local Government Minister Sandra Lee, a former Alliance colleague.
It caused great concern within the Alliance left, but Sandra Lee convinced them that the bill addressed their concerns.
She has argued that the bill is a statutory protection against water privatisation. She said that under it, local bodies "must not transfer ownership or control of significant water assets to anyone unless they are council-controlled".
"They are also banned from privatising the ownership of such council-controlled bodies," she said in a press release. "There are no ifs or buts or maybes around the words 'must' and 'must not'."
* During the 1999 election campaign, Prime Minister Jenny Shipley sacked Immigration Minister Tuariki Delamere after he refused to comply with her order to rescind a decision allowing certain investors into NZ at lower-than-usual minimums, as long as they invested in Maori enterprises.
