Visa Delta has written to a shortlist of agencies informing them it is starting a statutory review of its 5.5m media buying account.
It is thought the full 30m pan-European business may also be involved.
The account is currently held internationally by Zenith Media, while the creative work, which is not being reviewed, is held by Saatchi & Saatchi.
The account has been with Zenith since the Delta brand launched in the UK in 1993.
Visa has been running a campaign starring Mel Smith since September to educate users. It wants to convey to consumers that Visa Delta can replace cash as well as cheques. Visa claims the debit card brand is growing at a rate of about 30 per cent a year.
The Visa Delta debit card is funded by the consortium of UK banks that are part of the Visa network.
It is the biggest-spending part of the Visa brand because the banks, with their own branded credit cards, refuse to fund the Visa credit card brand.