Thousands of postal workers from London, Edinburgh, Bristol and other offices nationwide are striking as Royal Mail continues to push through huge job cuts.
The Communication Workers Union has branded Royal Mail's business approach "chaos management" after the company abolished 40,000 jobs.
But the Royal Mail has fought back against the CWU, saying it is angry the union has called on members to vote for a national strike - which would damage customer confidence and undermine the entire UK postal network.
If you're worried the strike will affect your post, Parcel2Go.com – Britain's largest online parcel delivery service – will be operating as usual.