Amazon staff at two Midlands depots have announced new strike dates marking one year of industrial action.
The GMB said more than 1,100 union members were expected to walk out at warehouses in Rugeley, Staffordshire, and Coventry next month.
Workers are calling for an hourly pay rise from £10.50 to £15 following a 50p per hour pay offer from Amazon for Coventry staff.
The retailer said it regularly reviewed its pay and offered competitive wages.
Union members in Rugeley are set to take part in a strike on 3 and 4 August, with the Coventry fulfilment centre seeing industrial action on 4 and 5 August.
This will bring the total days lost to strike action at Amazon this year to 26, the union said.
It marks the anniversary of the day hundreds of Amazon workers at a warehouse in Tilbury in south east England walked out in protest over pay.
Amazon’s minimum starting pay for employees would be between £11 and £12 per hour, depending on location, the company said.
Rachel Fagan, GMB senior organiser, said: “One year ago, Amazon workers downed tools in disgust after managers announced one of the world’s wealthiest companies would be offering a pay rise of just 35p.
“Twelve months on and Amazon is now facing the biggest week of industrial action in the company’s history – across two sites.”
A spokesman for Amazon UK said that in less than a year, its minimum pay had risen by 10% and by more than 37% since 2018.
They added: “We also work hard to provide great benefits, a positive work environment and excellent career opportunities.”