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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A mostly dry day but with a few showers, particularly during the evening.
A generally cloudy day, although some bright or sunny intervals are also likely.
A man from Northampton has found internet fame after a video of him failing to climb a wall on a Tough Mudder challenge went viral