Can a venue increase the service charge?

Well state sales tax is mandated by the state and not the venue. So, yes, a venue can change the sales tax if the state changed it. But 22% seems high. Is it the service charge that is changing?

Service charge and Sales tax are very different.

But check your contract, they can change their service charge fees if it's stated within the contract.

22% seems about right for most venues.

Are you sure you're not referring to a Service Charge?

Then, yes, it sounds like they are updating you to 2021 pricing. It is common for venues to update their pricing each year, so since you are choosing to move your wedding, my guess is that they are revising your service charge to 2021 rates.

They absolutely can, but I would lean on them to see if they'd help you out since you're probably rescheduling due to COVID-19. This is an unprecedented situation so lots of companies are making exceptions.