Hundreds of strikers outside Amazon’s Coventry warehouse were joined on Black Friday by trade unionists from Europe and the US as part of a global campaign calling for better working conditions at the internet retailer.

Wearing orange beanie hats branded with the GMB union logo, activists from Germany, Italy and California, on strike at their respective Amazon workplaces, expressed solidarity with the Coventry strikers, who have taken 28 days of industrial action since January.

Gathered on a grassy roundabout close to the vast warehouse in the chilly early morning air, scores of the activists from the Make Amazon Pay campaign joined in chants of: “What do we want? £15! When do we want it? Now!”

Jessie Moreno, who delivers Amazon parcels from Palmdale, in the California desert, said: “This isn’t just a US fight, this is a global fight, so we are happy to come here to support our brothers and sisters at the GMB.

“We have to spread the word and bring awareness,” he added. “The issues are the same, no matter where you are, no matter what country you’re in – it’s all the same.” Moreno described the challenges he faces at work of operating in high temperatures, to stringent targets.

“It’s the living conditions, it’s respect, and of course it’s money. We’re living in poverty conditions while the CEO, Jeff Bezos, gets richer and richer off our hard work, and we’re just struggling to put food on the table.”

Organisers at the GMB in Coventry, where workers first took strike action in January, say they have now signed up 1,200 members.

They made a formal bid for union recognition to the independent Central Arbitration Committee (CAC) this year, believing they represented more than half of the workers in Coventry. They subsequently withdrew the application, accusing Amazon of hiring up to 1,000 extra workers to “bust the union” after the CAC was understood to confirm Amazon’s claim that there were 2,700 staff on site. They are now considering a fresh application.

Standing with campaigners, Alke Bössiger, the deputy general secretary of the UNI global union, which is one of the co-convenors the Make Amazon Pay campaign, said: “It’s really important that people here know that they’re not lonely in this fight. It’s a long game, it’s not that we can achieve something overnight.”

She said 150 actions against Amazon were taking place in more than 30 countries on Friday. “Some of the actions are strikes and some of them are protests – on environmental issues, for example,” Bössiger added. “It’s such a big company and it has such a big global footprint.” She raised other issues including taxation, and claims of monopoly power.

The US regulator the Federal Trade Commission is engaged in a lawsuit against the company, accusing it of anti-competitive practices – something Amazon has denied.

In Coventry, the GMB has focused on winning higher pay, with action first kicking off last summer, after workers were offered a 50p-an-hour rise. Since then, the basic rate of pay has increased several times, and will rise to £12.30 an hour. Amazon denies the increases have any link with the industrial action, insisting it reviews pay regularly and always has.

Kate Bell, the deputy general secretary of the TUC, praised the long-running campaign at Coventry, telling the workers: “You guys are the future of trade unionism in the UK. You’re bringing people together and you’re only getting stronger.”

Rainer Raising, from Germany’s ver.di union, who is usually based near Bremen, also joined the Coventry workers. “We are here to show solidarity,” he said. “There’s a lot of action going on in Germany today, with nine or 10 places on strike. We’re asking for a decent living, and better conditions in the workplace.”

Gianpaulo Meloni, from Piacenza in Italy, where workers are on strike on Friday, is the president of the European Works Council, which brings together Amazon union reps from across the continent.

“At my site, we are fighting against Amazon since they came to increase the wage by just 1.1%. We were very upset. We started with a mobilisation, and we did some strikes this year – and today and tomorrow we are going to be striking,” he said.

Coventry workers shared stories from the early days of the strike, when the GMB only represented a few dozen workers.

“A lot of people were scared that if they started joining, they would end up losing their job – but I said, we can do better,” said one striker, Destiny Oebi. “It is a long journey – when the fire started, it was small, but it will get bigger and bigger, and it will be difficult to quench it.”

An Amazon spokesperson 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.”