Royal Mail workers have begun a one-day strike that is set to severely disrupt postal services across the UK.
The 24 hour strike which began at 03:00 BST on Friday morning is being observed by 130,000 members of the Communication Workers Union (CWU) in protest against a modernisation programme proposed by the postal service's management.
A spokesperson for the CWU said further industrial action could follow the one-day strike.
"We are prepared to continue to talk to Royal Mail but we have said to them that we have also agreed further strike action that is designed to take place within two weeks of June 29th if we can't reach an agreement."
The union is against the proposed modernisation of Royal Mail as it feels that the plan could lead to up to 40,000 layoffs.
Royal Mail contends that reform is needed to deal with competition after the postal services sector was opened up to competition last year.
It claims that modernisation is the only way to improve pay and provide better customer service.
A spokesperson for Royal Mail said the company was "hugely disappointed" by the strike.
The company has advised customers to post urgent mail early in the day and to use "one of the 14,000 post offices not affected by strike action".
Royal Mail added that all mail services except door to door, branch direct and same-day services would be affected by the strike. The backlog created by the strike will be addressed by prioritising items by the order in which they were received.
Private postal operators such as TNT and Business Post are likely to enjoy a day of bumper business as citizens feel the impact of the strike.