The House of Commons is due to debate a Conservative proposal to freeze the television licence fee for one year.
In April the annual fee for a colour TV licence went up by £3 to £142.50 - a 2% rise, linked to inflation - under the terms of a six-year settlement.
But the Tories say a freeze is needed next year if the BBC is to maintain public support in tough economic times.
BBC Trust chairman Sir Michael Lyons says the plan is "a recipe for curbing the BBC's editorial independence".
The Conservative proposal for a one-year freeze in the licence fee was announced by party leader David Cameron in March.
He said the BBC and other public bodies needed to maintain public support in the current economic climate by doing more with less.
On Tuesday, the BBC Trust's chairman told the Royal Television Society: "That is a recipe for curbing the editorial independence of the BBC.
"The traditional system of multi-year funding agreements... underpins the BBC's editorial independence."
Sir Michael said the tradition of setting the licence fee for several years meant the BBC's journalists did not have to trim their reporting to the prevailing political wind.
But shadow culture secretary Jeremy Hunt said Sir Michael had misinterpreted the policy, and that the issue was whether it was right for the BBC to taken an inflationary rise when there was no inflation.
During his speech, Sir Michael made reference to the usage of a potential surplus in cash allocated for the switchover to digital television in 2012.
Some of the licence fee has been set aside to help vulnerable groups with the change.
And it has been suggested that any leftover digital switchover money could be used to fund universal broadband as part of the government's Digital Britain plans.
But Sir Michael said research carried out by Ofcom suggested the public would like any surplus money to be paid back.
He said: "The licence fee should only be used to enable the BBC to deliver its public services.
"The digital switchover help scheme is consistent with that. The rollout and take-up of universal broadband may be consistent with that. We'll see.
"But taking licence fee payers' money and giving it to other causes and commercial players clearly isn't.
"It's wrong in principle, it undermines the BBC's accountability to licence fee payers, and it risks compromising the BBC's independence."
news.bbc.co.uk/1/hi/uk/8058637.stm
