The government was on Saturday scrambling to contact property owners affected by an administrative error that Labor has branded "a stuff-up of monumental proportions", where at least 140 new owners were not told they would be in the path of a future motorway before they bought.

And the government was forced to deny any link between the error and the ongoing outsourcing of services in the agency responsible, Land & Property Information, which is set to be privatised.

The Minister for Finance, Services and Property, Dominic Perrottet​, on Friday night revealed that buyers were given incorrect information when they did their due diligence with the government agency, potentially exposing the government to millions in compensation claims.

The error affects at least 140 properties purchased between June 27 and October 24 of this year that are in or near the planned F6 extension corridor in Sydney's south and the Werrington Arterial project.