They were particularly upset that their role in helping turn around the fortunes of the once-troubled gas company had not been publicly acknowledged, while the company directors had been praised by Ms Main.
"These are workers who had agreed to a pay freeze for four years. Now that things are going better, they've been able to have pay rises again," Mr Webster said.
He understood TrustPower would keep all the workers, but could only guarantee their jobs for two years.
"Their pay and conditions will be rolled over for that period."
He said staff appreciated that Ms Main and Mr Doyle had fronted up, but were not happy with the answers.
"The mayor said the council would do all it could to keep staff in Wanganui but, after that two years is up, who knows what will happen?"
Mr Webster was disappointed there had been no consultation with the union over the sale.
The sale will go unconditional in mid-June and TrustPower will take over on July 1. The council will retain GasNet, the infrastructure side of the business.