Amazon could be forced to recognise a trade union in the UK for the first time.
The GMB union says almost 700 Amazon workers in Coventry are now members.
It said this is more than half of the workers at the site – the usual threshold for mandatory union recognition in a workplace.
It comes after two weeks of strike action by workers at the fulfilment centre.
Amanda Gearing, GMB senior organiser, said: “GMB members have been crystal clear since the start of their campaign; they will not accept a pay rise of pennies from one of the world’s wealthiest corporations.
“After weeks of campaigning and 14 strike days, they’ve built the power of their union on site and are now in a position to file for recognition.
“Amazon top brass has refused to negotiate and now their own workers have forced them to the table.
“With industrial actions ballots under way in five further Amazon depots and more and more Amazon workers joining GMB, managers fast risk this becoming a summer of strike chaos for the company.
“The time has come for Amazon to sit down and talk pay with GMB Union.”
GMB said Amazon bosses have 10 days to respond and agree to voluntarily recognise the union, adding if this does not happen, they will start a statutory process through the Central Arbitration Committee.
In response, Amazon UK said: “We offer competitive pay, comprehensive benefits, opportunities for career growth, all while working in a safe, modern work environment.
“At Amazon, these benefits and opportunities come with the job, as does the ability to communicate directly with the leadership of the company.”
The company said it respects its employees’ rights to choose to join or not join a union and that it regularly reviews pay rates.
Over the past seven months, minimum pay has risen by 10% and by more than 37% since 2018, it said.
GMB union members at Coventry staged their first strike in January this year, the first official walkout to hit the US tech firm’s operations in the UK.
A number of other strikes followed until Amazon offered to increase the minimum starting salary of its UK workforce by 50p to between £11 and £12 per hour from April.
But this prompted an angry response from the union, which described the increase as “insulting” – its members had been calling for at least £15 an hour.