Council officers could soon have the power to slap fines of up to $5500 on large groups of people who do not purchase a permit to gather in Brisbane's public outdoor spaces.

Under a new proposal from City Hall aimed at protecting Brisbane's prized green spaces, groups of more than 50 who want to use any parks or open spaces citywide will have to pay more than $300 in advance for a permit or risk being fined.

Groups of more than 50 who want to use any of the city's parks or open spaces will have to pay more than $300 for a permit or risk being fined under a new plan

Labor councillor Shayne Sutton attacked the proposal's fee-or-fine structure, saying public spaces belonged to everyone in Brisbane.

"The size of your credit limit should not be a pre-determinant as to whether you can access a park for your birthday party," she said.