Waste Contractors and Recyclers Association of NSW executive director Tony Khoury said WSN had an unfair advantage because it was the only approved operator of the region's only tip, Lucas Heights.

Environment Minister John Robertson's office did not respond to the Leader's calls or emails.

Expressions of interest for a 20-year contract were extended to December21 after criticism that the time for tenders was too short.

The public exhibition for WSN Environmental Solutions's new Lucas Heights facility that would process up to 100,000 tonnes of waste a year on top of 575,000 tonnes for landfill closed yesterday.

WSN plans to begin construction of the facility next year and for completion by 2012.

A WSN spokesman said the facility would take waste from Bankstown and Parramatta councils and was "totally unrelated to any current waste-processing tenders''.

Mr Khoury said competitors were disadvantaged by an inability to access the Lucas Heights site and were unlikely to waste time and money tendering without a genuine chance of winning the work.

"If the intention is to obtain the best solutions and the best environmental outcomes, then access to the Lucas Heights site should be made available by the Government to all tenderers on the same terms and conditions as available to WSN.'' he said.