The Post Office said the majority of its branches were open despite the strike.
Three hundred branches are striking, but the Post Office said around 250 of these were open.
The rest of the Post Office's network of 11,600 branches is not involved in the dispute.
Post Office group network and sales director Kevin Gilliland said: "We want to reassure customers that nearly all of our network is unaffected by the strike action."
More top news
900 million people were registered to vote.
The wooden ship transported 110 people from west Africa to Alabama in 1860.
A total of 100 public order officers will be ‘strategically placed’ to deal with any possible disorder.