Royal Mail boss Moya Greene used the CWU conference on Wednesday to tell delegates to expect a fresh wave of job losses and closures in the race for privatisation.
In what was the first ever address to the union's annual parliament by a Royal Mail chief executive Ms Greene made backed the service's sell-off but denied that this approach would put profits before delivery and workers' interest.
Ms Greene claimed that the state had "starved" the business of cash and praised "good, loyal private investors who were only concerned about the success of the company."
She said that the postal service faced a "spiral of decline" because of unregulated competition from privateers such as TNT.
The Royal Mail has said that TNT's pilot service in west London underlines how competitors can cherry-pick the most profitable parts of the business with industry watchdog Ofcom's blessing.
She called for a closer working relationship with the union to beat off competition, adding: "The enemy is outside the company, not inside."
But her comments follow around 50,000 job losses in the past decade and 5,400 redundancies in the last year alone.
A series of conference debates this week have also highlighted an entrenched culture of work place bullying and harassment.
One Gloucestershire delegate invited Ms Greene on Wednesday to visit the threatened Gloucester mail centre and explain to the 450 workers why they were losing their jobs despite achieving all of the Royal Mail's efficiency standards.
Ms Greene blamed the closure on falling letter volumes and admitted more jobs will be lost in the future due to the ongoing restructuring programme that has already seen the number of mail centres across Britain slashed by more than half.
But CWU general secretary Billy Hayes attacked her for going along with the government's "we are all in it together" mantra and slammed her support for privatisation.
"Her big thing now is access to capital but we know the cheapest source of capital is the government," he said.
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