Workers at Felixstowe, the UK's largest container port, will go ahead with an eight-day strike after pay talks broke down.
Around 1,900 members of the Unite union will walk out on 21 August after rejecting an offer of a £500 lump sum on top of a 7% pay rise.
The Felixstowe Dock and Railway Company called the decision "disappointing".
Unite called for the port's bosses to make a "reasonable" offer, adding that it was open to further talks.
Unite's Robert Morton said: "Felixstowe docks is massively profitable. It can afford to put forward a reasonable pay offer to our members but once again has chosen not to. That decision was driven by greed not need."
A spokesperson at the port of Felixstowe said: "During talks yesterday [Monday 8 August] the port further improved its position offering a £500 lump sum in addition to 7%.
"The staff branch of Unite and the Police Federation of Felixstowe Dock and Railway Company have agreed to put a similar offer to their members. In contrast, the hourly branch of Unite has again rejected the port's improved position and refused to put it to its members."
Around half of containers brought in to the UK are transported via the port.
Our Customer teams are working hard to plan around the strike action where possible. We will contact you regarding any changes to specific bookings and will keep you updated as the situation develops.
Source: BBC News