Work is taking place today to add extra bays for season ticket holders to use at Stafferton Way car park in Maidenhead.
Commuters arrived this morning to find two levels taped off as contractors started updating signs and bays.
The Royal Borough said it hopes the work will be wrapped up today.
It means all four lower levels will be available for parking by season ticket holders only until 10am. Two were available previously.
The council approved the work after complaints there weren't enough bays available for drivers paying for permits.
The changes meant many motorists arriving at the car park today, most returning for the first time since the Christmas break, found no spaces were available.
A council spokesman said the work was scheduled for the first date available to contractors and permit holders can use other borough-run car parks while the Stafferton Way levels are out of bounds.
He added: "They don’t need to pay and display as they should already have a permit displayed on their windscreen."
Top Ten Articles
It's time to get voting as readers get their chance to decide the winner of the Independent Retailer of the Year at the inaugural Windsor and Maidenhead Business Awards.