The proposal, contained in a discussion paper on spending in local government elections, has infuriated the Liberal National Party, which described it as a plot to win control of Brisbane City Council.

The paper proposes capping mayoral candidate spending at between $30,000 and $250,000 depending on their number of constituents, while candidate spending would be capped between $15,000 and $30,000.

However, registered third parties such as unions or companies would be allowed to spend up to $3.8 million, either across all state local government areas or in just a single council like Brisbane.

“This cap can be applied flexibly across local government areas,” the discussion paper says.

Lord Mayor Adrian Schrinner, who’s a Liberal National Party member, slammed the discussion paper proposals as a Labor plan to oust him.

Schrinner said the caps would allow individual unions aligned to the Labor Party to each spend $3.8 million at the next Brisbane City Council election, due in 2024.

He said he supported a system of fair spending caps however the current proposal – which would allow a union to spend more than four times the amount of a registered political party at the next Brisbane City Council election in 2024 – was outrageous.

“If the Labor Government was serious about electoral reform, it would have consulted with councils and come up with something fair,” he said.

“Instead, it’s produced a 30-page plan to rig the next Brisbane local government election through a farcical financial gerrymander.”

LNP integrity spokeswoman Fiona Simpson called the discussion paper “a brutal assault on democracy” and accused the state government of planning “blatant election rigging”.

“While mayors and councillors will have their campaign spending significantly capped, the unions will be able to pour millions of dollars completely unchecked into any community they like,” she said in a statement.

“In short, every other political party or independent candidate will be forced to fight for their beliefs with one hand tied behind their back, while the Labor Party and the unions will be allowed to play by their own rules.”

Deputy Premier Steven Miles said the proposed caps were similar to state election rules, and were higher than the amount most candidates spent on average in past elections.

He also insisted the discussion paper was not a formal plan, but instead the start of a conversation about spending caps.

“Feedback, including from the LNP and Lord Mayor, will be considered in determining what caps the government ultimately proposes,” Mr Miles told AAP in a statement.

“The paper very clearly asks ‘Do you support the proposed cap for registered and unregistered third parties?’

“There has been no decision made on electoral expenditures caps, other than to begin a consultative process.”

However, peak body the Local Government Association of Queensland has also expressed concerns.

LGAQ chief executive Allison Smith said elections should be fair, democratic and free from undue influence.

She said any changes to campaign spending rules should create an opening for unfair distortion by third parties.

“Councils across Queensland have called for any new campaign spending cap regime to be accompanied by new laws to prevent the potential distorting influence of any proposed spending caps by third parties with aligned interests,” Smith said.

“We urge the government to ensure any proposed changes reflect this intent.”