TORONTO -- Ontario's Liberal government is looking to limit the influence of third parties during elections, a year after advertising by those groups in the last provincial vote topped $8 million -- unions among the biggest spenders.

The province is currently the only jurisdiction in Canada -- of those that regulate third-party advertising -- that does not impose limits on advertising spending or contribution. The government promised in the recent provincial budget to strengthen the rules.

Treasury Board President Deb Matthews' office says the government will propose limiting contributions to third parties, regulating election-related, third-party spending and increasing reporting requirements.

"I think we all think that it is time to take a look at that, what kind of regulations should there be, what kind of limits on donations, that sort of thing," Matthews said Monday. "I think it's to the point where we need to take some action."

The number of third parties has more than tripled since 2007 and spending has increased by more than 400 per cent to $8.4 million, Ontario's chief electoral officer said in his report on the 2014 general election. Greg Essensa has been calling for third-party election advertising to be reined in for years.

"This lack of regulation is creating an uneven playing field that can potentially influence electoral outcomes," he wrote.

Unions were some of the largest third-party advertisers during the last election. The Working Families Coalition, known for its anti-Tory ads, spent $2.5 million during last year's campaign, with contributions from some of the province's biggest unions.

The Ontario English Catholic Teachers Association spent $2.2 million and the Elementary Teachers' Federation of Ontario spent $1.3 million, records show.

Progressive Conservative Bill Walker said as a candidate during an election he is at a disadvantage against groups with deep pockets.

"Other groups can come out and outspend me 20:1 -- how do you compete?" he said. "They can control the airwaves, they can control the messaging in the papers. It just isn't fair."

Candidates can spend $1.28 per elector, so if there are 100,000 potential voters in an electoral district a candidate can spend $128,000.

NDP Leader Andrea Horwath said it's important "for a variety of voices to engage in the public debate" during elections, but it's time to look at making the rules more fair and transparent.

The government is also planning to amend government advertising legislation to require the government to submit preliminary ads for the auditor general to review, define "partisan" in relation to its advertising and restrict government ads during elections.

It is already a long-standing practice for government to limit its advertising during election campaigns to routine or urgent matters, but the government indicated in the budget that it would legislate that.

In addition, the Liberals said in the budget they would allow the auditor general to review online and digital advertising -- something that was less of a concern when the laws came into effect in 2004. In 2013-14, the government spent $12 million on digital advertising, compared to $13 million on TV and $6 million on print, Matthews' office said.