Much of the nation's post passes through London on its way elsewhere, so if they come out on strike the ripple effects could disrupt deliveries across the country.

BBC: NEWS | Business | Q&A: Postal pay dispute

"They had been engaged in the process from 18 months to two years of discussion with government and management and now, suddenly, they present memoranda and say you have got 14 days to come to an agreement with our demands otherwise we are going to go out on strike, " Ian Phillips, a special adviser to Public Enterprises Minister Jeff Radebe, told the BBC's World Business Report.

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