Energy regulator Ofgem has asked five suppliers to pay what they owe a renewable energy fund or risk having their licenses withdrawn.
The regulator said the feed-in tariff was not paid by Colorado Energy, Igloo Energy Supply Limited, Neon Reef Limited, Whoop Energy Limited and Symbio Energy.
Between them they owe £ 765,000.
The deadline to contribute to the program, which supports small renewable energy producers, was last Friday.
Not contributing to the fund is a violation of supplier licensing requirements, and if suppliers do not pay, Ofgem said it could strip them of their rights to provide gas and electricity to homes.
They could also face a fine, Ofgem said.
It comes amid a surge in gas prices that has put pressure on the entire energy supply industry.
Many suppliers have contracts that require them to sell to customers at a fixed price for a year – a price that is now much lower than what gas costs companies to buy.
Larger suppliers have insured against large price fluctuations by purchasing their gas in advance, unlike many smaller suppliers.
Some commentators have speculated that less than a dozen of the roughly 50 vendors in the market will still be in business by the end of this year.
Five other suppliers have already closed in recent weeks.
In recent years, many vendors have gone out of business in the fall as FIT and other payments come due.
Not being able to contribute to the FIT or the revolving bond scheme has in the past been seen as a sign that corporate finances are under pressure.
Earlier Tuesday, Bloomberg reported that Igloo – which has the largest unpaid FIT payment – and three other energy providers had stopped taking new customers.
Business Secretary Kwasi Kwarteng and Ofgem boss Jonathan Brearley met with suppliers on Tuesday to discuss their situation.
However, Mr Kwarteng previously said there would be no bailouts in the area.
Colorado Energy still owes £ 261,406, Igloo owes £ 316,582, Neon Reef owes £ 37,351, Symbio Energy owes £ 146,239 and Whoop owes £ 3,780.
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