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Most businesses can re-open when the country moves from lockdown to a lower alert level on Tuesday, but they must follow strict heath and safety rules.
CTU president Richard Wagstaff said people returning to work would likely be stressed about being exposed to Covid-19 and their employers must protect their physical and mental health.
"The essential service workers and now the level 3 workers, they're our first people going out there and putting themselves at risk to keep things going, to keep businesses going, to keep their work going.
"We owe it to them to make sure that we do everything we can to make sure they're looked after."
It was more important than ever that businesses have procedures in place for reporting health and safety problems when they arise, he said.
Employers also needed to reassure staff who needed to stay home that they would retain their pay.