The Independent Television Commission is to allow Channel 4, Channel 5, Flextech, GMTV and Sky to pool their sales arrangements.
An ITC consultation document states that it will drop restrictions on joint selling of national airtime to 'lessen concerns about the potential market power of the Channel 3 sales houses'.
The change is subject to a consultation period, with the regulator seeking responses from licensees, advertisers and media buyers by January.
The move means that TV stations can open talks about merging sales operations, although decisions on this area are likely to be made after the consultation period is over.
The consultation document states that the ITC intends to continue the ban on Carlton Communications and Granada Media establishing joint airtime selling arrangements.
The ITC said that the changes have been proposed in light of the power of the two ITV sales houses, which control 60 per cent of TV advertising.
One senior executive said he was keen to make sure that the ITC 'imposes punitive measures should ITV be found to be breaking the rules'.
In a separate move, the ITC has announced plans to develop a new framework for commercial television as digital platforms take off.
The ITC is streamlining with around one in ten jobs expected to go.
The streamlining comes ahead of a government white paper which may recommend the abolition of the ITC in favour of establishing a super-regulator.