Postal workers at the Royal Mail sorting centre in Filton, Bristol are starting strike action this morning.
Up to 1,000 workers are expected to take part in the official strike which will disrupt collections in the BS1-10, BS13 & BS14 postcode areas of the city.
This latest industrial action is part of a long-running dispute over pay, conditions and cuts to the service.
The strike is set to end at 2000 BST on Friday, according to the Communication Workers Union(CWU).
David Wilshire, Bristol and District Branch Secretary, said: "The strike action is in response to Royal Mail ignoring agreements with the Trades Union."
"A ballot was conducted and a 70.6% yes vote was returned."
A Royal Mail spokesman said: "Having met the union more than 50 times in recent months, it is increasingly clear that the CWU refuses to believe that mail volumes are declining.
"This is despite the clear evidence of this in the UK and in every other postal market around the world."