Britain's Guardian newspaper reported last week that dozens of Nepali workers had died on building sites while the ITUC said on Friday that 4,000 lives would be at risk before a ball was kicked at the tournament.
On Tuesday, the Brussels-based ITUC said Qatari authorities had promised "simply" to increase the number of labour inspectors.
"Qatar response to labour rights violations weak and disappointing," said ITUC general secretary Sharan Burrow on Twitter.
"There are already labour inspectors and they have no impact," she added on the organisation's website (http://www.ituc-csi.org).
"What is needed are laws that protect workers' rights to join a union, bargain collectively and refuse unsafe work, and only then can inspectors do their job.
"The laws in Qatar give employers total control over workers so no worker will feel able to speak freely to a labour inspector."
Burrow said many workers suffer exploitation for fear of retaliation if they speak out.
"We have taken the step of lodging a case with the International Labour Organisation describing how Qatar's work visa system allows employers to use forced labour," she added. "The spotlight is now fully on Qatar's abhorrent labour practices.
"It has taken two years to get this far and pressure will need to be sustained if lives are to be saved and dignity restored."
The ITUC said on Friday that mortality figures for workers from Nepal and India, who account for most of the 1.2 million migrant employees in Qatar, show that on average 400 of them die each year.
On Monday, officials from Nepal and Qatar sought to play down the Guardian report and held a joint news conference to say the migrant workers were "safe and fully respected".
Qatar won the right to host the tournament in December 2010, winning the vote ahead of Japan, South Korea, United States and Australia.
FIFA said last week that it was concerned by the allegations and would discuss the matter at an executive committee meeting on Thursday and Friday.
The international players' union FIFPro said it was "deeply alarmed" and called on Qatar to deliver the tournament in accordance with "football's universal values".