In its response to the Government's Green Paper on charter renewal, the regulator, which many believe will have a strong influence over future legislation, argued that the likes of Channel 4 should be able to stake a claim to a share of an increased licensed fee to avoid the BBC becoming the UK's sole public service broadcaster.
The Ofcom response comes just two weeks after a claim by BBC chairman Michael Grade that the idea of so-called "top-slicing" of the licence fee would be a threat to the BBC's political independence.
"Ofcom believes that if the public service system as a whole is to continue to have wide influence and impact in the future, it is essential that the BBC is not allowed to become isolated in a growing – and exclusively commercially focused – sector," the regulator said.
"If the BBC were to become the UK's sole public service provider, there is a risk that audience tastes would be conditioned by the commercial majority, rather than the public service minority."
Grade told the Westminster Forum two weeks ago that top-slicing would "seriously weaken" the BBC's ability to invest in content "at a time when the provision of public service programming from other public service providers is in doubt."
C4 has said it needs more investment from the public purse in the future if it is to continue PSB services without its content suffering.
The channel would be the major winner if Ofcom's argument is accepted. Ofcom this week had more good news for the commercial sector.
It gave the go-ahead for ITV to slash its non-news regional TV commitment by as much as half as part of its review of public service broadcasting.
Ofcom plans to allow the broadcaster to hack back in correlation to digital switchover.