The firms owe £17.9 million in total to the so-called renewables obligation scheme.
Ofgem has warned seven suppliers that they need to pay into a renewables scheme or face having their licences ripped up as a spike in the gas price pushes many companies to default.
The energy regulator said the seven firms still owe £17.9 million to the so-called renewables obligation (RO) skema. The money is due for final payment by Sunday.
In past years, companies who have struggled to pay into the levy – which is designed to encourage renewable energy – have often collapsed shortly afterwards.
With gas prices having risen up to five-fold since the start of the year, more than a dozen energy companies have already collapsed in the last two months.
Earlier this month Ofgem issued a warning to five companies about their RO payments.
Since then two of those suppliers have gone bust, while another paid up in full.
Ampower and Whoop Energy, who were named earlier this month, are yet to pay up.
Ofgem also warned five other suppliers after they failed to assure the regulator they would pay their dues in time.
Delta Gas and Power Entice Energy, MA Energy, Neon Reef, and Together Energy have been sent so-called provisional orders from Ofgem.
If they do not pay, Ofgem might rip up their licences.
Only suppliers who do not source enough of their electricity from renewable sources, or do not buy enough so-called Renewable Energy Guarantees of Origin certificates, have to pay into the fund.
Gas prices are spiking because of high demand out of Asië low wind speeds – which have meant more gas being burnt to generate electricity – and a global economy that is rebounding as pandemic restrictions ease.