The future viability of the Mayo Power plant in Killala is now in question, following the decision of the energy regulator to issue a Certificate of High Efficiency to the company with a rate of 18% - compared to the 100% issued previously.
Some €95 million has already been spent on the €255m high-efficiency combined heat and power plant in Killala.
Work on the plant was halted in 2016 when one of the investors withdrew from the project.
New investors then came on board to complete the 45 megawatt biomass-fuelled power plant, and they applied for the necessary consents.
Renewed consents were was given by Mayo County Council, the EPA and ESB Networks, while the energy regulator has taken since last May to respond.
The high efficiency rating of 18% now issued by the regulator puts the commercial viability of the project in question, according to Mayo Senator Michelle Mulherin.
The FG Senator believes the energy regulator has a number of questions to answer in relation to this power plant, and she's calling for the regulator to appear before the Oireachtas Committee on Communications, climate change and the environment to answer these queries.
Senator Mulherin says this is a very important project for north Mayo, and is also of national importance as it will help Ireland acheive its targets on renewable energy.
The FG Senator says this latest development calls into the question the viability of the Mayo Power plant.
A spokesman for Mayo Power confirmed to Midwest News that the project promoters will discuss this latest development later today, but are unlikely to issue a statement on the matter yet.