Saints have announced they have already sold their allocation of Amlin Challenge Cup final tickets.
Northampton and Bath were both given close to 1,000 tickets for the event at the 12,000 capacity Cardiff Arms Park on Friday, May 23.
The ERC started selling tickets in September, meaning there are limited numbers for the two finalists.
Saints gave season ticket holders who attended last Friday’s semi-final win against Harlequins priority and all of the allocation was sold inside the first 24 hours.
“The club appreciates any disappointment that this news may bring,” a statement on the club website read.
“There is a possibility that further tickets will be released by ERC; in the event that this happens further announcements will be made.”
The shortage of tickets will leave many supporters without the chance to attend the showpiece event, while those who are heading to the Welsh capital face a hotel headache.
Rooms in Cardiff are few and far between, with the ones available costing more than £200 for the night.