Victoria's political donation laws must be more stringent to eliminate the perception that politicians can be bought, the state's Ombudsman has said.

The comments came as an investigation cleared Casey councillors Geoff Ablett and Amanda Stapledon of receiving campaign donations from property developers in return for favourable planning decisions.

The pair stood as Liberal candidates in the 2014 state election.

While the allegations were unsubstantiated, Ombudsman Deborah Glass said they posed questions about the propriety of donations made by developers to political campaigns.

"There can be little doubt that the lack of transparency in political donations and the lack of limitations on who can make those donations in Victoria creates an environment in which allegations of improper conduct can flourish," she said.

"Ultimately, they create a perception that politicians can be bought, which reduces public trust in government."

Victoria and Tasmania are the only jurisdictions without donation disclosure rules for candidates standing for state election.

Federal laws require donations over $13,000 to be disclosed to the Australian Electoral Commission.

New South Wales laws banning property developers from making political donations were upheld by the High Court last month.

'Urgent' reforms needed before next election

The Victorian Ombudsman's investigation found the councillors received campaign donations from property developers with considerable interests in the municipality.

"One property developer had 610 planning applications before the council over a two-year period, and made donations to the councillors' political campaigns of $44,000 and $32,575," the report said.

Ms Glass said urgent reforms were needed before the next election.

"We should not wait for a scandal for this to happen," she said.

Greens MP Ellen Sandell will introduce a bill to Parliament next month to try to ban council candidates and political parties taking donations from property developers.

"It's clear that Victoria has some of the weakest political donation laws in the western world," she said.

"I don't think property developers would donate to political parties unless they were getting something out of it, unless they were getting some kind of benefit.

"There's huge potential for corruption."

Planning Minister Richard Wynne said all political parties must comply with donation disclosure laws.

"I have never taken one cent from a developer," he said.