bbc.co.uk | Last Updated: Wednesday, 19 December 2007, 01:42 GMT
Broadband firms could face formal action if they fail to give consumers accurate information about the speed they will get when they sign up.
The warning comes from Ofcom as it moves to ensure that net firms do not oversell broadband in advertising.
Customers should get specific data about the speed on their line or be able to back out of the deal.
The regulator said new guidelines on the selling of broadband should come into force early in 2008.
The warning came in a letter sent by Ofcom boss Ed Richards to the Ofcom Consumer Panel in response to its work with broadband suppliers on the advertising and selling of high-speed services.
In his response Ofcom boss Ed Richards backed the consumer panel work and said it was talking to the broadband industry about how best to implement the recommendations.
The result of these discussions should be made public early in 2008, he said.
"We are keen that any measures are implemented in the shortest time frame possible," said Mr Richards. "At this stage, we have not ruled out the possibility of using formal powers if we consider it would be more effective in delivering our objectives."
A spokeswoman for Ofcom said that currently the regulator had no powers to enforce the new arrangements on the selling of broadband but would seek them by beefing up the guidelines net firms must abide by.
"This is a considerable consumer issue we are concerned by," said the spokeswoman. "We think consumers should get what they pay for. It's an important decision for them."