International unions on Thursday slammed 2022 World Cup host Qatar over the treatment of migrant labourers and condemned what they call the systematic exploitation of workers at sporting events worldwide.
"Qatar is a slave state," said Sharan Burrow, head of the International Trade Union Confederation (ITUC).
Speaking on the sidelines of the annual congress of the International Labour Organization (ILO) -- the UN's labour agency -- Burrow said little real action had been taken to improve labourers' working conditions.
"We haven't unearthed the worst of it yet," she said.
Migrants, mostly from South Asia, form over 90 percent of the labour force in Qatar, where 88 percent of the population is from outside the country.
Human rights campaigners Amnesty International say they are treated like "animals," with hundreds dying on construction sites.
The ITUC warns that at current rates, as many as 4,000 might be killed by the time the tournament kicks off.
The energy-rich emirate is also facing swirling claims that corruption played a role in the surprise decision by world football's governing body FIFA to name it host of the 2022 showcase.
"The danger now is that the corruption issue -- which is very serious of course -- is going to overshadow the situation of workers on the ground," Burrow warned.
Long-running concerns have been given fresh impetus by the World Cup drive and Qatar's breakneck economic development.
Burrow said workers' living conditions in Qatar were all too often squalid, with inadequate food and medical care.
Qatar's "kafala" visa-sponsorship system handcuffs foreigners to their local employer.
South Asian workers pay middlemen huge sums to win a work permit, and fear that complaining will mean getting fired and deported -- if their employer even agrees to an exit visa.
Domestic workers, mostly women, who suffer abuse also struggle to free themselves from employers.
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"How can we allow, as human beings, that Qatar can have a World Cup when they are still abusing domestic sector and contract workers," said Myrtle Witbooi, chair of the International Domestic Workers Network.
The International Transport Federation has also filed a complaint against Qatar Airways at the ILO over its treatment of white-collar employees.
- Devil in the detail -
Global unions have repeatedly locked horns with Qatari authorities, who say they are striving to improve the situation.
Under mounting pressure, Qatar in February issued fresh guidelines on workers' rights, but the ILO has urged it to go further.
The emirate has said it plans to abolish the kafala system.
"It remains to be seen what they will replace it with. The devil is in the detail. Announcing is very easy to do," said Francois Crepeau, the UN's migrant rights monitor.
"But years of international scrutiny due to Qatar asking for and obtaining the World Cup will prove useful. We'll see what happens," he added.
Unions say Qatar is an extreme example of a wider problem surrounding the globe's increasingly expensive sports events.
Workers all too often pay the price for high-pressure, multi-billion dollar drives to get ready, they say.
"We should focus on the workers, who make the beautiful game possible," said Ambet Yuson, head of the Building and Wood Workers' International.
Nine workers have died on stadium projects in Brazil, where the 2014 World Cup kicks off on June 12.
The picture was similar for the 2012 European football championships in Poland and Ukraine.
Six died in Poland and 14 in Ukraine, where shadow employment left many workers unprotected, said Vasyl Andreyev, head of Ukraine's construction union.
In contrast, the stadium toll for the 2010 World Cup in South Africa was two, and zero for the 2006 edition in Germany.
Five have died on 2018 World Cup host Russia's stadium sites, but concerns are rising because of the use of easily-exploitable migrant workers, said Yuson.