Hospital workers' unions are opposing increased car park charges at Grantham, Lincoln and Boston hospitals. They say there has been a lack of consulation with staff and the increases are excessive.
Unions said there is no indication about where the extra money will be spent, but it should go towards improved security in car parks.
Hospital managers say they are sticking to the increases from a typical �2 to �3 per day across the sites.
They say shoppers are abusing the car parking facilities and running them has been a drain on funds.
Lincolnshire's Patient Forum wants a compromise needs to be found.