The campaign against the Government's controversial plan to privatise Royal Mail won more support as unions warned potential investors against buying into the sell-off.
The TUC Congress in Bournemouth gave its backing to the Communication Workers Union and Unite, which are fighting privatisation on behalf of more than 100,000 postal workers and managers.
The CWU's deputy general secretary, Dave Ward, said he was confident his members would vote in favour of strikes when they are balloted in the coming weeks.
He told delegates that postal workers had dealt with some difficult issues as the industry has changed and modernised in recent years, adding: "We have not gone through all of that pain to save the industry only to hand it over to private investors who will take more money out than they will ever put in."
Mr Ward said he also had a message for Labour leader Ed Miliband, who is pressing for changes to the party's links with union.
"I go to sorting offices up and down the country and workers there are not talking about a new relationship. When are you going to get off your backside and stand up for a great public service like the Royal Mail?" said Mr Ward.
The union will take its campaign to the floor of Labour's annual conference in Brighton later this month, said Mr Ward, adding: "We have a warning for investors who might be thinking they will come in for a quick killing - we are not going away, we will defend the postal service and our members with everything we have got."
Tony Burke, assistant general secretary of Unite, which represents managers, said the public strongly opposed privatisation, adding: It is clear the Government is motivated by the chance to make a quick buck, a chance to sell off one of our prized assets at a massive cost to the taxpayer."
Mr Burke asked what safeguards the Government had put in place to stop stamp prices increasing or to safeguard the universal services.
"Will a private company keep an eye out for pensioners and the disabled as postal staff do on their rounds? Will they walk the floors of tower blocks to deliver mail?
"The Government should dump the idea, admit they got it wrong and admit they have no mandate."
A Department for Business spokesman said: "Action taken by the CWU will not alter the Government's decision to sell shares in Royal Mail in this financial year.
"Parliament decided over two years ago that selling shares in Royal Mail was the right thing to do to secure Royal Mail's future and protect the six day a week, one price goes anywhere, universal postal service. A successful, financially sustainable Royal Mail with access to private capital is in the best interests of the workforce and all users of the universal service.
"The Government accepts that it will not be able to convince the CWU of the benefits of a sale. But it believes that its reforms - including a sale of shares - will ensure that Royal Mail has a sustainable future.
"A viable and successful Royal Mail is in the best interests of employees. Through the sale we are also giving employees the opportunity to own a real stake in the business.
"We would encourage the CWU and RM to agree a pay deal through negotiations. This will be in the best interests of the employees, the company and, ultimately, the users of the universal service."