Jim Reeves, from the Communication Workers' Union, says the argument to close 70 Crown Post Offices is flawed because the business is profitable.
He spoke to ITV News Central outside the Kings Heath branch in Birmingham as staff went of strike this morning.
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Cloudy and breezy through the night with increasing amounts of low cloud and some outbreaks of rain.
The rain will ease for a time across most parts, but further locally heavy rain will spread in from the west.
It really does seem like it mainly rains on the weekend. This week it's been quite fresh with sunny days, the weekend will be wetter.