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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Any mist or fog will clear during the morning to give another dry day with light winds and some sunny spells.
The bus was travelling along Hale Street when it collided with a number of stationary cars and a lamppost before crashing into Sainsburys.
Rescue teams dashed to Trinity Street in Coventry shortly after 6pm after the Stagecoach bus crashed into the front of the store.