Vicky Kloss, City's director of communications, was attempting to make contact with manager Roberto Mancini ahead of his TV interviews before Sunday's FA Cup tie when she was told by a steward she would not be allowed into the players' tunnel.
City claimed she was told she was being denied entry because she is a woman, which Notts County deny.
More angry words were exchanged after the 1-1 draw.
The episode came just eight days after Richard Keys and Andy Gray engaged in their infamous criticism of assistant referee Sian Massey at Molineux.
Notts County denied the claims from City, insisting Kloss was not prevented from entering the area because of her gender, but because she did not have the right pass.
A County spokesman said: "It's nothing to do with her being a woman. She was trying to get into an area without the correct accreditation."
However, it has been established that Kloss' junior colleague, who is male, had been allowed to enter the same area five minutes earlier without being asked for a pass, which he did not have anyway.
City are so incensed about the manner in which their staff were treated that they intend to write to County chief executive Jim Rodwell for an explanation.