Migrant workers building infrastructure for a new city in Qatar which will host 2022 World Cup matches are still suffering exploitation and severe human rights violations despite promised government reforms, according to a highly critical report by Amnesty International.

The report names an engineering company, Mercury MENA, which it says left almost 80 workers from Nepal, India and the Philippines stranded and unpaid for months in Qatar. Amnesty accuses the company of using the kafala structure – which it describes as Qatar’s notorious sponsorship system that ties employees to a single employer – to exploit scores of migrant workers.

In Nepal, 34 people told Amnesty they were owed on average £1,500 by Mercury MENA, and that the kafala system was used to exploit them. One worker said the company had finally agreed in October 2017 that he could leave to work for another company in Qatar, but that in return for that permission, required under kafala, he had to renounce his claim for unpaid wages.

Last October, Qatar’s government committed to work with the International Labour Organisation (ILO) on wholesale reform of kafala and substantial elements of its labour laws after years of sustained criticism highlighting human rights abuses relating to migrant workers. This month the emir of Qatar issued a law abolishing, for most workers, the power of employers to grant or withhold exit permits, which were used to prevent people from leaving the country.

However, Amnesty argues that the central exploitative problem with kafala remains, which is that workers are tied to a single employer, and that reform through the ILO process is happening too slowly.

“The exit permit is just one key of Qatar’s notorious ‘kafala’ sponsorship system. This system has fuelled widespread abuse and exploitation of migrant workers, including forced labour,” Amnesty said.

“Although today most workers no longer need their employers’ permission to leave the country, they still need a ‘non-objection certificate’ from their employer to change jobs in Qatar. Many employers refuse to provide such certificates, and workers are forced to stay until their contracts finish, which can be up to five years.

“Workers who leave their jobs without employer permission can be reported for ‘absconding’, attracting a criminal charge that could lead to arrest and deportation. This is in contravention of international labour laws and standards.”

According to Amnesty, Mercury MENA worked on an infrastructure project – although not directly on a World Cup project – in the new city of Lusail in Qatar’s capital, Doha, which will host a showpiece stadium where the 2022 World Cup opening match and final will be held. Workers said they began to have problems being paid by the company after a corporate reorganisation in 2015. Amnesty said it was calling for the Qatari government to ensure the employees receive the money they are owed, “while ensuring there are fundamental reforms to the kafala sponsorship system”.

The ILO said the Qatar government had made substantial progress on its three-year “technical cooperation programme” to ensure “compliance with ratified international labour conventions as well as achieving basic principles and rights related to work in Qatar”.

The abolition of the need for exit visas for the majority of workers “marks the removal of a major element of kafala,” the ILO said, and the government recently committed to further dismantling the system next year, allowing people to move jobs freely. A number of significant structural changes introduced by Qatar, the ILO said, include the adoption of a temporary minimum wage in October 2017, improvements to the health and safety regime, an inspectorate system, and establishing dispute resolution committees to deal with workers’ complaints. Qatar also said a fund would be set up to pay staff wages where employers have not done so, although it is expected to apply retrospectively to only one year’s pay and so is unlikely to compensate the Mercury MENA workers.

The ILO said it would “continue to work with the government of Qatar as well as representatives of employers, global unions and other partners to ensure that the goals of the cooperation programme are met”.

Amnesty said in its report that Mercury MENA, which it described as “ailing”, had not responded to its concerns since November, nor to a summary of its findings sent to the company in July. At the time of writing, the Guardian had not received a reply to emails sent to the company.

• This article was amended on Wednesday 26 September at 08:22 to make clear that the affected workers were not employed directly on World Cup projects.