Bucks Council was formally served legal papers last Friday (July 16) by the Hampden Fields Action Group (HFAG), disputing the 3,000 home development in Aylesbury.
The Council has until next Thursday July 29 to respond to a Pre Application Protocol Letter (PAP) questioning the approval process.
The HFAG claims local NHS groups in Stoke Mandeville and Wycombe objected to the proposals.
The action group set up a fundraiser to raise money to legally challenge the council on the development.
The fundraiser received over 300 donations and reached nearly £38,000 in just seven days.
It would cause major traffic disruption if the new homes were built, the action group says. It would mean 48,000 vehicles per day using the main road in Hampden Field, the group says.
Speaking to the Bucks Herald in May Phil Yerby who set up the group said: ""The public will notice that the Hampden Fields facilities are woefully inadequate and no services whatsoever have been provided on Kingsbrook thus far which has put immense pressure on Poplar Grove and Oakfield surgeries.
"This is unacceptable. The council approved plans are so inadequate that the NHS are saying that no facilities will be built on either Hampden Fields or Woodlands.
"Add to that no facilities are currently anywhere near being delivered for Kingsbrook."
When the proposals were approved last month developers said they would invest £72 million on facilities.
It said plans were in place to deliver two new primary schools, a new doctor's surgery that will be capable of further expansion, employment land for up to 1,200 new jobs, over 109 hectares of green open space, sports and play facilities, allotments and community growing spaces.