They said the inclusion of the indoor recreation centre in the previous budget was a "community contract" that had prompted them to spend time and money on putting together a business case with plans and funding models.
The model included Wintec providing land at its Avalon Drive campus valued at $2 million for the centre with the remainder of the money coming from trusts, naming right sponsors and fundraising.
The centre, previously described by Sport Waikato chief executive Matthew Cooper as a big shed with a good floor, would comprise nine netball/basketball-sized courts, 200 car parks, changing rooms, spectator seating and storage and administration space.
The trust was unhappy with the council's decision given it had worked closely with the council on the project and had altered its proposal as a result of the council's financial problems. The new proposal required the council to fund half of the building and committed the trust to raising the rest.
"This facility has been mooted for more than a decade. The people of Hamilton have again missed out on a community indoor sporting facility to encourage fitness, wellbeing and social enjoyment by people of all ages," the letter said.
In a dig at the $68.4 million Claudelands Events Centre, which had originally been planned to include the indoor sports centre before being changed to an arena for high-level sports, the trust said: "It is not a 'luxury item', but a piece of basic community infrastructure of a modern city."
The council was also urged to be "open-minded" to any other opportunities around the project which might come up.
The community centre's constituent management group includes representatives from the region's sporting groups such as Sport Waikato's Mr Cooper, Netball Waikato's Ben Sinnamon, Cam Mitchell from Waikato/Bay of Plenty Football, Hockey Waikato's Declan Wyndham-Smith and Volleyball Waikato's Dave Macpherson, who is also a city councillor. Volleyball Waikato has previously said the lack of community sporting facilities in the city has curbed the sport's growth.
The trust declined to elaborate on the letter, saying it was private.