The Greens party room has hardened its opposition to Labor’s signature heavy industrial and resources emissions reduction plan, for the first time overtly declaring it must include a specific ban on new fossil fuel projects.

While the party says it still has concerns about other parts of the government’s so-called safeguard mechanism reforms including “rampant use of offsets”, the Greens said they were prepared to back the scheme if “Labor agrees to stop opening new coal and gas projects”.