The state government has been accused of diluting a promise to replace thousands of existing trees lost to be uprooted for Westconnex with saplings no taller than ballpoint pens.

While it is yet to provide final designs, the government plans to link the M4 and M5 tollways with an interchange up to 65 metres deep and with three levels of tunnels in the inner-west.

A contractor removing trees at Sydney Park to make way for the WestConnex motorway. Credit:James Brickwood

But an unreported change to the 7.5-kilometre tunnels between Haberfield and St Peters, or the third stage of Westconnex, has been a dilution of a promise to replace the vegetation lost to construction.

"The replacement trees are to have a minimum pot size of 75 litres," the community was told about the project last year. The government had promised to plant 3500 replacement trees of that size.