As the nation burns more coal to replace lost nuclear capacity, power producers are able to duck pollution standards by building coal-fired projects small enough to avoid national regulator scrutiny, critics say.

About a third of 45 new power-generation units fueled by coal won't face the government's environmental assessment because their small size puts them under the review level, according to Kiko Network, a Kyoto-based environmental group.

Coal's role is under debate as resource-poor Japan grapples with the Fukushima disaster's shutdown of all nuclear plants and plans to cut greenhouse gas emissions. While operators say smaller plants can be built faster, their exemption from national-level inspections is a sore point for foes.