Electoral law experts have told a parliamentary committee there should be a set date for elections, rather than the government in power deciding when they are held.
Associate Professor Andrew Geddis from the University of Otago said the date should be fixed in law, and an early election should only be called when a majority of MPs voted in favour of it.
He told the special select committee dealing with the Electoral (Finance Reform and Advance Voting) Bill a government with majority support would still be able to use its voting power to call an early election.
"However, the Government will only be able to achieve its ends openly and following a full debate on the matter in the House, which will impose a political cost that may counteract any political advantage gained," he said in his submission.
The bill replaces the Electoral Finance Act and sets the rules for running elections, the money that parties can spend and election advertising.
It does not deal with the date for elections, which has always been a decision made by governments and can be chosen at a time which best suits them.
In a separate submission a group of experts made the same point.
"While even a legally fixed election date can be avoided and an early election called...the political costs of doing so likely will be higher than under the present system, whereby the matter remains entirely at the prime minister's prerogative," they said.
"To hold an early election, the Government would be required to explain to the public why it is acting in a manner other than specified in law."
The group included Victoria University's Professor Jonathan Boston, constitutional lawyer Mai Chen and 11 others.
They said Canada had legislated for a fixed date for its national and provincial elections, while the recently formed coalition government in Britain had promised to do so.
The Labour Party said the bill should require greater transparency of party funding, which it has raised in the past.
The party also criticised the lack of spending limits for parallel campaigners -- organisations other than political parties.
"This has the potential to skew an election result in favour of the best-resourced campaigns -- especially if the interests of political parties and parallel campaigners are aligned," it said.
The New Zealand Law Society said electoral finance provisions in the bill remained "discouragingly complex" and it needed a comprehensive redraft.
"People should be able to work out in advance whether they can do something, and not have to get a legal opinion first," said the society.