The Berejiklian government has defended moves to rush through legislation to keep open a coal mine in Sydney's catchment despite impacts on water quality, with one minister declaring, "if you want a friend, get yourself a piece of coal".

The legislation, aimed at nullifying a Court of Appeal ruling in August that declared the extension of the Springvale coal mine invalid, was expected to pass the lower house on Tuesday and be voted on in the upper house on Wednesday.

Chris Jonkers of the Lithgow Environment Group at East Wolgan swamp, which has been extensively damaged by subsidence from the underground coal mine. Credit:Wolter Peeters

Planning minister Anthony Roberts lugged a large lump of coal into question time and placed it on the dispatch box while answering a question about the bill that aims to ensure coal supplies to the nearby Mount Piper power plant are not disrupted.

"This amazing piece of black rock keeps you cool in summer, warm in winter, it produces power to power electric motor vehicles," Mr Roberts said, echoing theatrics by the Turnbull government in February.