Pompey's ticket office will be undergoing planned maintenance from 5pm on Tuesday, July 23 through to the afternoon of Wednesday, July 24.
Tickets and hospitality will be unavailable to purchase online, over the phone and in person during this time.
Season ticket holders with 5+ loyalty points will now be able to purchase tickets for the Sunderland away fixture from 1pm on Wednesday, July 24.
The club apologise for the inconvenience.