A protest by gas installers and plumbers will take place outside the Dáil today to highlight the number of unregistered people working in the sector.
The Association of Plumbing and Heating Contractors of Ireland claims a survey has shown that up to 60% of work is carried out by gas installers who aren't registered with the RGII.
They are calling on the energy regulator to take more action against those operating within the black market.
Sean Giffney, chairman of the APHCI, said it is a dangerous trade for people who don't know what they are doing.
"The Consumer Association of Ireland ... estimate that there were more than 27,000 boilers installed in 2011, and out of that, there were 15,000 of these boilers that were installed illegally," he said.
"And we don't know how safe those boilers are."