Internet providers will have to advertise minimum download speeds NBN customers can expect at peak times or potentially face prosecution, under new guidelines set by the consumer watchdog.

The Australian Competition and Consumer Commission (ACCC) has moved to protect NBN customers from misleading broadband speed offers, paving the way for providers to be prosecuted for misleading claims, such as ads using 'best-case- scenario' broadband speeds.

ACCC chairman Rod Sims said the guidelines will bring 'enormous benefits'.

'Advertising, and the way the industry speaks to consumers will go from meaningless to meaningful,' Mr Sims said.

The guidelines, published Monday, offer retailers standards for advertising speeds - including clearly identifying typical minimum speeds during the internet rush hours of 7pm and 11pm.

Mr Sims said advertising is 'unacceptable' in the context of the forced migration to the NBN.

The new standardised labels aim to provide clarity about what speeds consumers have actually bought and offer a way to compare providers.

'It's a game changer because the retail service providers will have to tell the truth,' Mr Sims said.

'With this guidance, if you buy a 'Basic evening speed' plan you should generally not expect speeds much different to your pre-NBN experience.

'If you buy 'Standard evening speed' or higher plans, you should expect certain minimum speeds during busy periods.'

'It is not acceptable to advertise an 'up to' speed claim, as this can give the false impression that the speed advertised is achievable at most times,' Mr Sims said.

'The guidelines signal a sea change for consumers and RSPs (retail service providers) - that they'd better lift their games,' Mr Sims said.

Teresa Corbin, CEO of consumer representative group the Australian Communications Consumer Action Network (ACCAN), said consumers are unable to tell what speed to expect from a service .

'The ACCC has recognised the frustrations consumers experience when services don't work as advertised and expected, and is suggesting that retail providers can do better in these areas. ' Ms Corbin said.

Mr Sims said the worst offenders could face prosecution and said if the industry did not 'lift its game' the commission will seek government intervention.