Councillors have been warned if they do not allow a development in Moseley they may face a legal bill and maladministration charge.
On 10 February councillors refused permission for a Tesco store and medical centre on St Mary's Row.
The development comes before the planning committee again on 3 March.
But lawyers for developers Exmax (Moseley) Ltd have warned any appeal would be successful and their chances of winning costs "substantial".
They added they would also make an official complaint "as refusal of planning permission is so unjustified as to be likely to amount to maladministration."
The comments are recorded in the planning committee notes to go before councillors in March.
The development would include a Tesco store, medical practice, 14 sheltered apartments and parking.