Labour chief Chris Sun said on Saturday that the government plans to introduce new guidelines to protect workers from heat stroke by April next year.
Officials have been studying whether to add the Observatory's heat index as one of the references for the guidelines.
Speaking on RTHK, the minister said officials would likely consult the affected sectors in October, although he said he had reservations about classifying heat stroke as an occupational disease.
"The question we have to ask is, are [workers] being exposed to much higher risk of being infected or suffering from a particular disease as compared to the general public? It's not," Sun told reporters after attending radio programmes.
"Based on the evidence available to us, it's very difficult for us to say that for some of the workers, in some professions, or work types, they're more susceptible to heat stroke."
Sun said in the past year, two prosecutions had been made over heat stroke, involving employers who are suspected of not having provided cool drinking water to workers.
That's out of some 26,000 inspections made by the Labour Department.
Both the Federation of Trade Unions and the Federation of Hong Kong and Kowloon Labour Unions have called for laws that require the suspension of outdoor work when the temperature reaches 39 degrees Celsius.
However, Sun said while Guangdong province has similar laws, he said it might not be good for Hong Kong to have such "one-size-fits-all" legislation, saying the heat index is more objective.