The new leader of one of Britain’s biggest unions has vowed to take on Amazon by plotting an international campaign to unionise its warehouses and improve conditions for its workers.

In an interview with the Observer, Sharon Graham, who became Unite’s general secretary last week after a shock victory, said she was in talks with unions in Germany and the US – Amazon’s other major markets – to effectively form a global union campaign that would “pincer” Amazon and force it to allow workers to organise themselves more freely.

Graham said she wanted to deploy “leverage” tactics deployed against difficult employers to convince Amazon to sign a “neutrality agreement”, a document guaranteeing that warehouse workers can form a union without fear of repercussions. The campaign would include lobbying governments in all three countries to use their power as major Amazon customers to pressure it into action.

“I’m talking to the German unions and the American unions because we’re their three biggest markets in both [web services] and e-commerce,” she said. “Let’s work together to get Amazon organised in those three countries. If we do that, we could actually pincer them simultaneously in their three biggest markets. Once we get a neutrality agreement, those workers will join the union. They won’t now because they’re too frightened – they think they’re going to be sacked.

“What I would say to [Amazon founder] Jeff Bezos is he should treat workers fairly, come to the table and sign the neutrality agreement. Eventually, it will have to happen. We’re not going to get bored. If this takes two years, it takes two years. Resources will be allocated. Because if we don’t do that, you ignore the beast who is pace-setting bad behaviour. He may as well come the quick way around. We’re in for the long haul. We could actually crack Amazon. And that would be an amazing thing.”

Amazon has repeatedly been accused of refusing to recognise unions. Last year, the TUC compiled a document in which it said workers had described gruelling conditions, unrealistic productivity targets, surveillance, bogus self-employment and a refusal to recognise or engage with unions unless forced. The company has disputed the claims.

“We respect our employees’ right to join, form or not to join a labour union or other lawful organisation of their own selection without fear of retaliation, intimidation or harassment,” said a spokesperson.

“Across Amazon we place enormous value on having daily conversations with associates, and work to make sure direct engagement with our employees is a strong part of our work culture. The fact is, we already offer excellent pay, excellent benefits and excellent opportunities for career growth, all while working in a safe, modern work environment. The unions know this.”

Graham, who used her leadership campaign to say she wanted to end the union’s heavy involvement in the running of the Labour party, said Keir Starmer’s office had already been in touch about holding a meeting with her following her victory. She said she would demand to know what action Labour was taking to end “fire and rehire” practices.

“I won’t be talking about the leadership of Labour. I won’t be talking about the internal wranglings of Labour. I’ll be talking about fire and rehire, and what is Labour going to do about that issue? When and how are they going to step up to the plate? The Labour party aren’t in power at the moment. A parliamentary Labour party is not going to stop job losses, they’re not going to stop suppression of pay, they’re not going to stop what’s happening to workers out there. So it is not my number one priority.”

She also said that while she would continue to pay the fees Unite hands Labour to be affiliated to the party, any future additional funds would be conditional on Labour being able to prove it was helping Unite’s industrial priorities.

“I will not just be handing over cheques in addition to our affiliation to the club without understanding how that progresses the lot of workers,” she said. “I’m going to be asking, ‘so what are you going to do?’ There won’t be anything additional unless, of course, I can show that it’s important for progressing workers’ issues. I hope Labour do that, because that is part of what they’re there for.”

Graham said she would reform the union into sector-by-sector “combines” – a move designed to increase the union’s power with the most powerful employers.

She said she was “very proud” of the leverage tactics she has deployed against hostile employers, which sees the union target a company’s commercial vulnerabilities such as potential contracts, shareholders or acquisitions, in order to further its goals. She said her “non-traditional” methods were required because persuasion and argument did not work with hostile employers.

“We do a very, very detailed research document looking at every aspect of the company – shareholders, clients, future clients, investments,” she said. “We get into the sinews of the money. We think, ‘OK, what’s more important to them than what they’re trying to do here?’ It’s accountability. Where an employer moves from what I would call normal, acceptable behaviour into very hostile terrain, like sacking workers and then re-employing them, I don’t think we can stand by and watch that happen.

“I will be very deliberate and serious about the plans that we put in place around public sector pay, for example, but also around the private sector. We need to make sure we protect jobs, terms and conditions. And I’ll do anything we need to do to do that.”