The visitor attraction's managers have submitted an official objection to proposed free parking next to the recently opened £7m footbridge over the River Hull.
They say allowing motorists to park for free at the car park in nearby Tower Street could "affect the financial stability" of The Deep, which operates its own pay-and-display car park.
The objection, which will be considered by city councillors next week, says the free car park could lure some visitors away from using The Deep's own car park, giving them only a limited time to enjoy the aquarium's facilities.
Planning permission was granted for the Tower Street car park with a condition that free parking was provided for two hours.
A report for next week's meeting admits other car parks where charges currently apply will be hit by the new free facility.
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