Qatar World Cup monitors have found workers going more than four months without rest on building sites.
The Impactt audit highlights Qatar's ongoing challenge improving working conditions as it prepares to host the FIFA showpiece in 2022.
At eight of the 19 contractors assessed, working hours exceeded 72 hours per week which Impactt described as a "critical" non-compliance of expected practices.
Three workers for one contractor went without a day off for between 124 and 148 consecutive days. One extreme case reported a 402-hour working month, 90 hours over the limit.
Impactt does acknowledge a "new spirit" in Qatar to embrace changes to labor laws.
After finding 96 percent of new workers paid an average of $1,248 for their jobs, World Cup organizers repaid 10 percent of the workforce.