Olympic-branded gear – to be worn by British athletes and Games volunteers – is being manufactured for Adidas in sweatshop conditions in Indonesia, making a mockery of claims by London 2012 organisers that this summer's Games will be the most ethical ever.

With just over 100 days to go before the Games begin, an investigation by The Independent has uncovered widespread violations of workers' rights in Indonesia, where nine locally owned and managed factories have been contracted to produce Olympic shoes and clothing for Adidas – the official sportswear partner of London 2012 and of the British team.

While the German company – which unveiled its Stella McCartney-designed kit for British athletes last month – hopes to make £100m from its Olympic lines, the mainly young, female factory employees work up to 65 hours (25 hours more than the standard working week), for desperately low pay. They also endure verbal and physical abuse, they allege, are forced to work overtime, and are punished for not reaching production targets.

None of the nine factories pays its employees a living wage – about 20 per cent higher than the official minimum wage – one of the cornerstones of the Ethical Trading Initiative (ETI) base code, an internationally recognised labour code adopted by the Olympics organising committee, Locog. Workers struggle to survive on pay as low as 5,000 rupiah (34p) an hour, skipping meals to save money, and sending their children away to be looked after by grandparents.

The ETI base code – which Locog says must be complied with by all companies supplying goods to Olympic licences – also stipulates freedom of association. Yet workers allege that some unions are not given bargaining rights by Adidas's Indonesian suppliers. At PT Shyang Yao Fung, in the industrial city of Tangerang, west of Jakarta, 10 workers were suspended a month ago – and face being laid off – because of their union activism, they believe.

Even for those with jobs, conditions at Taiwanese-owned Shyang Yao Fung – which produces women's sports shoes – are poor, according to workers. While business has been slow lately, employees – whose basic pay is 1.53m rupiah (£105) a month – have in the past been asked to work five hours of overtime a day, they claim.

"The management says that overtime is compulsory," said Sobirin, 32, wolfing down a plate of nasi goreng in a Tangerang café. "And there are many times when workers are working without payment on overtime, or are not paid properly. Every day there's a worker who passes out because they're exhausted or unwell."

At another Tangerang factory, PT Panarub Industry – Adidas's main global supplier of football boots, and outfitter of some of Britain's Olympic footballers – workers are proud to have shod David Beckham, Frank Lampard, Lionel Messi and Zinedine Zidane. However, in common with workers at other factories, they say they face intense pressure to meet production targets.

"It's hard to get permission even to go to the bathroom; we're tied to our seats," said Yuliani, a 23-year-old seamstress, speaking metaphorically. "If you're forced to go, the pile of work becomes so high that you get shouted at by the production line leader. They call you a dog, brainless, uneducated. Sometimes we have to sacrifice our lunchbreak to reach the target."

Her colleague, Ratna, added: "If the leader gets really angry, they throw the shoes in front of the workers. Once on my line I saw a worker get hit by a shoe."

Some workers described being slapped in the face and having their ears pinched by managers. At PT Pancaprima, in Tangerang, supervisors use a loudspeaker to berate production lines hourly for failing to meet targets. "It's humiliating," said Margi Wibowo, 41, who works in the warehouse.

At PT Golden Castle, in Jakarta, workers have to eat their lunch outside, squatting on the ground, near a rubbish tip. "It's really smelly sometimes, and it's near the port, so it's very dusty," said Surati, 32. "When the wind blows, the rice gets mixed up with the dust."

At PT Golden Continental, which is not an Olympic contractor, workers who fail to reach targets are locked in a room and made to stand for hours on end, according to Jamiatun, a union leader. "In the past, the whole production line was locked up," she said. "Now it's just the slow individuals."

The sweatshop allegations follow the resignation of Meredith Alexander, one of Boris Johnson's "ethics tsars", over the awarding of a stadium contract to Dow Chemical, the current owner of Union Carbide Corporation, responsible for the 1984 Bhopal gas disaster.

None of the Indonesian employees had heard of the ETI base code, and none knew about Locog's complaints mechanism, set up to enable workers to report labour violations. This is hardly surprising – as recently as February, Locog had yet to disseminate its information material in factories, and had translated it only into Mandarin.

The Independent was told that four of Adidas's Indonesian suppliers pay less than the minimum wage for the garment industry.

Adidas said in a statement yesterday that only one company paid less. It added that excessive working hours were "an exception, not the norm," and that overtime had to be voluntary.

In relation to Shyang Yao Fung, the company said it had learnt only three days ago that "several" union officials had been laid off, along with 150 other workers, "due to a factory downsizing". It said it was aware only of isolated cases of harassment or abuse, and was "disturbed" by the allegation of workers being locked up for not meeting targets. The Commission for a Sustainable London 2012, the body responsible for monitoring ethical practices relating to the Olympics, said last night that it was "deeply concerned" about the alleged infringements of Locog's sustainable sourcing code.

Shaun McCarthy, the commission's chairman, said: "The allegations uncovered by The Independent are of serious concern.

"The priority for Locog must be to investigate these issues and act accordingly to protect workers' rights and improve working conditions."

Locog said: "We place a high priority on environmental, social and ethical issues when securing goods and services and take these allegations extremely seriously.

"We have spoken to Adidas and they have assured us that they are investigating these allegations, the conclusions of which will be made public."

The six Indonesian factories did not respond to requests for comment. A spokesperson for Stella McCartney declined to comment.

Ethical sourcing? The factories

Tangerang city hosts four factories – PT Panarub, PT Pancaprima, PT Shyang Yao Fung and PT Tuntex – which supply Adidas with Olympics-branded goods. PT Golden Castle in north Jakarta, the capital, pays the equivalent of 55p an hour.

Case Studies

"Every month I have to borrow, so I'm getting more and more into debt."

Mirna

Mirna would love to go to the London Olympics, but the airfare alone would cost her half a year's wages. The closest she'll come is stitching jackets and T-shirts emblazoned with the jagged 2012 logo.

Mirna works for PT Golden Castle, earning 8,125 rupiah (55p) an hour. For the 39-year-old widow, life is a daily struggle. She has had to send her 13-year-old son, Madrim Maskuri, to her home town, near Cepu, in East Java, to be looked after by his grandparents.

"It's difficult," she says, gesturing at her home – a tiny, bare room with peeling walls, a single naked lightbulb, a plastic closet and a gas hotplate – in a crowded back alley traversed by skeletal cats and open drains. "Every month I have to borrow, so I'm getting more and more into debt. And I really miss my son: I only see him once a year, because the travel is so expensive."

Mirna shares her 8ft by 8ft room with her adult son, Rahmadi. They share a bathroom with two other families in the tumbledown warren of streets. What does Mirna wish for? "I want to live decently with better conditions. I want to live like everyone else does."

"Ethical? I don't think so. The only privilege is we work harder than ever."

Siti Hadijah

Siti Hadijah pulls out a notebook and shows me two columns of figures. One lists her regular expenses: rent, electricity, food and so on. "The other is one-offs, like my friend is getting married soon and I have to buy her a wedding present," she says. "I've no idea how I'll afford it."

The shy 32-year-old, who wears a Muslim headscarf, works for PT Tuntex in Tangerang, stitching jackets, shorts, trousers and polo shirts, all carrying the Olympic logo. "I feel proud and happy to be making Olympic goods, but the work is really hard and the supervisors try to force us to reach targets," she says.

Like many garment workers, she came to Jakarta to find work, in her case from Nusa Tenggara, a group of islands near Bali.

"If we only work 40 hours a week, with no overtime, things are really tight," she says. "And I'm single. What about people with families?"

On hearing that the London Games are being vaunted as the most ethical ever, Ms Hadijah laughs and looks bemused.

"I don't think so," she says. "The only privilege – if that is the right word – is that we need to work harder than ever."

Quotes

Jacques Rogge

President of the IOC, March 2012

"[London has] raised the bar on how to deliver a lasting legacy, and set out a blueprint for future host cities to aspire to"

Paul Deighton

London 2012 Chief Executive, November 2008

"Our ambition is to set new sustainability benchmarks for the way large-scale events are staged – the Sustainable Sourcing Code is a key part of this"

Lord Coe

London 2012 Chairman, Dec 2008

"We are seeking to set new benchmarks for Olympic Games, Paralympic Games and major global events"

Tony Blair

Prime Minister, July 2005