“The bosses at Amazon consistently have refused to get the message or listen to what their workers are saying,” said GMB senior organiser Stuart Richards.
“We’ve had a series of strikes at Coventry already and each time we do it we get more and more workers come and join us on the picket line.”
Workers in Coventry first walked out in January – the first ever strike by Amazon employees in the UK.
Members are calling for an hourly pay rise from £10.50 to £15 following a 50p per hour pay offer which was branded “derisory” by the union.
However, the union is not recognised by Amazon and GMB told the BBC that as a result, there were no discussions between the employer and its staff.
“The fact that Amazon consistently refuses to have a discussion or listen to concerns adds fuel to the fire,” said Mr Richards.
“Each time we take strike action we feel anger and resentment to the fact that the bosses are refusing to listen to them at all.”
He said more and more workers were joining the union – which now has 700 members at the site representing about half the workforce.
However, Mr Richards believes Amazon “ignoring” striking workers was “starting to backfire” and two more sites, in Macclesfield and Rugeley, were being balloted for industrial action.
“At some point it’s going to get to the point where the impact on their business is so significant they’re going to have no choice [but to negotiate],” he said.