Under the scheme, launched in June 2005, local authorities can declare that residents living in defined zones no longer wish to accept cold callers at their homes, including representatives of charities.
Charities fear the zones could affect cash collections and fundraisers recruiting direct debit donors (Third Sector, 20 September 2006).
The OFT is looking into the legal status of the scheme after a working party that included representatives from the Public Fundraising Regulatory Association and the Direct Selling Association raised concerns.
An OFT spokeswoman said: "We are working with key stakeholders to find a solution that balances the need to protect the vulnerable while ensuring honest businesses aren't penalised."
Bedfordshire County Council, which established the first county-wide no-cold-calling zone in January, is speaking to Hertfordshire County Council about introducing zones and how they can be enforced.
Matthew Deaves, senior communications officer at Bedfordshire County Council, said: "We can't prevent someone trading, but if a resident calls us we can invite traders to leave."