The appalling conditions faced by thousands of migrant workers building the infrastructure for the 2022 football world cup in Qatar have not improved despite a growing outcry, according to the International Trade Union Confederation [ITUC].

Human rights organisations, Fifa and the European parliament have raised concerns about the plight of migrant workers in Qatar after a Guardian investigation revealed a rising toll of death, disease and misery at its World Cup construction sites.

But after a four-day visit to the country by an ITUC delegation, the organisation's general secretary, Sharan Burrow, said they had found "no improvement in living and working conditions" of migrant workers.

"This is an easy choice for the Qatari government. The perplexing question is, why won't they take it? Professional and poor workers alike tell the same stories; they came to Qatar with optimism and goodwill, only to face despair when their employer decides they are disposable and refuses to pay wages, sacks them without benefits, and/or refuses to sign their exit permit."

Burrow said that during the visit the 11-member delegation held worker hearings and were shocked by "tales of terror", stories increasing numbers of women and children in detention centres, and rising discontent and unrest in workers in "squalid labour camps".

"What we've seen this week can be summarised as how not to design a system for the global workforce on any basis: human and labour rights; goodwill and international reputation or; productivity based on loyalty and efficiency," said Burrow. "International companies should be on notice about the reputational risk of doing business in Qatar without respect for workers' rights."

The Guardian first reported on the plight of migrant workers in Qatar in September. The investigation revealed that 44 Nepalese workers died from 4 June to 8 August this year, about half from heart failure or workplace accidents.

Workers described being forced to work in 50C heat without drinking water by employers, who withhold salaries for several months and retain their passports to prevent them leaving the country.

The investigation found that sickness was endemic, that conditions were frequently overcrowded and insanitary, and that many were going hungry.

The ITUC has warned that as many as 4,000 migrant workers could die before a ball is kicked in 2022, while an in-depth Amnesty report last month revealed fresh evidence of wide-scale and endemic mistreatment of workers, many of whom are tied to their employer under the kafala system.

Football's governing body, Fifa, has said: "Fair working conditions with a lasting effect must be introduced quickly in Qatar", and president Sepp Blatter admitted that widespread abuse of migrant workers was "unacceptable" following a meeting with international union leaders in Zurich.

The Qatari authorities have insisted they are being proactive and say the World Cup can be a catalyst for change.

Burrow said: "Fifa have called for the improvement of core international labour organisation standards and an end to the kafala system. They will report back in March 2014. We can only hope the Qatar government will make the right choice."