Employers who do not follow the Manpower Ministry's health advisory for the haze could be penalised, Acting Manpower Minister Tan Chuan-Jin said on Sunday.

He said in general, if employers do not protect their workers, they will be investigated under the Workplace Safety and Health Act. "If the workers are working outdoors and they are expected to work with masks, we expect that to be adhered to. If there are circumstances where they are not, then that's something we have to follow up on with the companies," he said.

He added that the ministry is working with the Health Ministry to distribute protective face masks to companies that need them.

Asked whether the Ministry would consider halting work for specific groups such as outdoor construction workers when the three-hour Pollutant Standards Index crossed a threshold, he reiterated that the government is basing its health advice on the 24-hour forecast.

"I know that when we see the PSI spike and the haze is particularly thick we tend to get panicky, and that's perfectly understandable... but it's the cumulative exposure over the course of a day that has the real impact," he said.

The 3-hour PSI reading as at 11am on Sunday was 90, which puts it in the moderate range.