"This happened because submissions were only able to be made over the summer period when churches were busy in the lead up to Christmas, and with clergy and staff then on leave, and because council wrongly assumed it had consulted trade unions," he said.
"In my view ... the process the council did undertake favoured the business community so that the council received an incomplete and biased response to its proposed policy".
Before 1980 New Zealanders enjoyed more than 100 shared leave days, and "losing one of the very few now remaining guaranteed shared leave days is a significant matter for society as a whole."
He said a petition "of over 400 people asking council to hold a proper and fair hearing was ignored, leaving court action as the only remaining resort for natural justice on this issue".
This was presented to council in October, when he requested a new hearing be held before December. At the time, councillors discussed whether a different hearing date could be scheduled due to staff workloads.
Yesterday, Napier Mayor Bill Dalton said he was aware of the judicial review being applied for, but would not comment further as the matter was before the courts. Gwynn also said he would not comment.
His action was applauded by Napier resident Isabel Morgan, who had opposed the policy with a statement read on her behalf at the 2017 meeting when it was adopted.
Yesterday, she said she supported Gwynn, as she thought the council had not considered the church, or wider community during the consultation process.
"I think we have to pursue every avenue we can," she said. "If we're passionate about it, we should follow through."
She had opposed the policy as she thought there were already too-few days a year when families could spend time with each other without the distraction of shopping.
Napier's Waiapu Anglican Cathedral dean Ian Render said he had heard of angst about the policy but, being new to the role, did not feel he could speak on behalf of his congregation.
Napier and Wairoa are the only councils in Hawke's Bay to allow Easter Sunday Trading.
Last year both Hastings and Central Hawke's Bay district councils resolved to retain the status quo.