Supporters of a radical new way of electing Ontario politicians will today announce the formation of a Yes campaign for the Oct. 10 referendum.

The move comes one day after the Liberal government released regulations for the vote that place no limits on how much any group can spend to promote or oppose the system.

"We expect that some individuals and groups will want to campaign in favour of one system or the other," Democratic Renewal Minister Marie Bountrogianni said in a statement.

"It's important that this debate be open and transparent. That's why the government has set rules for referendum campaign advertising," she said.

But in a welcome development for the well-organized and funded Yes side, there will be no spending cap. Thus far, there is no organized campaign to support the status quo.

Referendum voters will be asked if they support replacing the first-past-the-post system with mixed-member proportional representation (MMP).

In the new system, there would be a two-part ballot in which voters would choose MPPs in 90 newly created, larger ridings instead of the current 107 constituencies. An additional 39 MPPs would be selected from party lists to reflect the popular vote and would be awarded to parties proportionately.

The referendum requires a 60 per cent "super majority" of all votes cast and would also have to be approved by more than half the ballots cast in at least 64 of 107 ridings. Any changes would take effect in 2011.

Under yesterday's rules, which apply to the campaign period that starts Sept. 10, a referendum group would have to register with Elections Ontario if it spends more than $500 on ads.

The lack of a spending limit means someone with deep pockets could "buy" a result for one side by flooding Ontario with ads, warned Progressive Conservative Leader John Tory.

In news conferences this morning at Queen's Park and in Ottawa, the Vote Yes for MMP campaign will be formally launched.