In June a planning inspector found the council's draft core strategy unsound because the housing targets it contained depended upon housing growth that a neighbouring North Hertfordshire District Council no longer intends to deliver.
The planned expansion - known as the Stevenage and North Herts Area Action Plan - formed part of the East of England Plan that the last Government approved and which is technically still in force.
North Hertfordshire suspended work on a joint project to deliver the homes in June 2010, following communities secretary Eric Pickles' announcement of his intention to abolish regional spatial strategies (RSSs).
During the inquiry into Stevenage's core strategy, North Hertfordshire council advised the planning inspector that its new plans would be unlikely to provide for Stevenage's planned growth.
Stevenage Council said this convinced the inspector that the growth of the town planned in its draft strategy was "undeliverable".
However, a Court of Appeal ruling in June on the long-running CALA Homes case concluded that councils cannot take the Government's intention to scrap RSSs into account when formulating local planning policies.
Stevenage has now launched a legal challenge to the inspector's ruling on this basis.
The council said it has made several attempts to get the inspector’s decision overturned and has asked the Planning Inspectorate to withdraw his report, but they have refused to do so.
It said it has also asked the secretary of state Eric Pickles to overrule the decision but he said he does not have the power to do so.
The council said it had now asked the High Court to overturn the inspector’s decision and grant an interim declaration that it is not required to withdraw its draft Core Strategy.
No date has yet been set for a hearing.