The Cambodian health ministry said seven labourers died after mixing the alcohol with water and soft drinks.
After returning from Thailand, the workers were placed in a quarantine camp in northwestern Banteay Meanchey province.
They complained of headaches, dizziness and difficulty in breathing after drinking the mix on Tuesday and Wednesday.
Experts collected the samples and took them to a laboratory in Phnom Penh for an analysis.
Cambodia began to reopen this month, announcing a phased reopening to fully-vaccinated foreign tourists from 30 November.
The program will allow those visitors to skip quarantine if they stay at least five days in designated areas, the Tourism Ministry announced.
The first such areas are two seaside provinces, Sihanoukville and Koh Kong, on the Gulf of Thailand.
On arrival, visitors must show proof they have been vaccinated and take a rapid results test for COVID-19. They can proceed without quarantine if the results are negative.
Cambodia has recorded some 119,000 coronavirus cases and 2856 deaths since the start of the pandemic.