Royal Mail workers say that it is about their rights and the modernisation of the service, but this week's postal strike is expected to take its toll on small businesses.
Furthermore, if workers' demands are not met, the union has warned of two more possible strikes over the summer.
The disruption caused to small businesses is likely to have a more devastating effect than on larger businesses, because any business lost as a result of late deliveries represents a larger percentage of their profits, industry experts have warned.
Clive Davenport, of the Federation of Small Businesses, added: "A lengthy postal strike would be devastating for small businesses.
"Our survey on the postal service showed 88 per cent of small firms send mail every day and 94 per cent of small businesses use Royal Mail exclusively. A cheque delayed in the post can mean the difference between life and death for a small business."
