Small contractors have urged the government to ensure they are not cut out of the market for work on its Green Deal.
The UK Green Building Council and the Federation of Master Builders said large companies must not be allowed to gain a stranglehold on the market.
The Green Deal is the centrepiece of the Energy Bill, which was published last month.
Under the scheme, set to be launched in late 2012, households take out loans to make energy efficiency improvements and pay back the money through a charge on their energy bills.
Retailers, local authorities and builders’ merchants will be able to advise people on the best energy efficiency measures for their homes, arrange the deal and installation, and even carry out the work themselves.
More detail on how accreditation and financing will work is expected in secondary legislation in the first half of 2012.
But construction bodies fear high street retailers and councils may subcontract the improvements to just a few big firms, leaving small companies in the cold.
An FMB spokesman said: “Our main concern is opening up the market to SMEs to make sure work is not just done by Marks & Spencer subcontracting to larger contractors.”
He suggested some smaller contractors might not want to arrange loans for householders and added that extra incentives might be needed for householders and businesses to carry out improvements.
A spokeswoman for the Department of Energy and Climate Change said there should be a range of contractors carrying out Green Deal work.
The Energy Bill includes an obligation for energy firms to contribute towards the cost of upgrading homes of people on low incomes or with hard-to-treat properties from 2012.