"The enemy of my enemy is my friend", or at least this appears to be the case, as opposition to the state Government's CBD Metro Project continues to build.

The new line, which is estimated to cost 5.3 billion dollars, will extend heavy rail from Central Station, through the city and out to Rozelle in the inner west.

This week's release of the Environmental Assessment Statement, for the underground line, was met by a wave of outrage from right across the political spectrum.

Liberals, Greenies and unions all joined forces this week at a mass rally at Parliament House in Macquarie Street.

2SER's David Fanner was there.