Anyone who lives with a Covid-19 case but does not have the disease themselves must remain in isolation for at least 10 days after the case is released from isolation.

That tallies up to a total 24 days, assuming the household contacts do not themselves catch the virus or that nobody else in their home catches it.

The new rules, introduced on Friday, are part of the government's strategy to slow the spread of Omicron in the community but how employers and employees will manage the lengthened isolation period is already raising concerns.

Employment lawyer Barbara Buckett, of BuckettLaw, said it's unclear how people who can't work from home can stretch their existing leave balances over the 24 days.

"It really is a compulsory leave situation which may or may not comply with the sick leave requirements and certainly 24 days is going to exhaust most people's sick leave," she said.

Buckett said businesses will also struggle when one or more employees are forced to isolate at home for the nearly-four week period.

"Particularly small businesses, to sustain a small business like hospitality with a loss of, and we're not just talking possibly one employee we're talking probably many as people are saying because it's like a domino effect, and 24 days is not sustainable," she said.

It's estimated up to 350,000 people could be isolating at home at the peak of the Omicron outbreak; some able to work from home but many, such as those working in retail, hospitality or trades, will not.

After announcing the shift to the 'red' traffic light on Sunday, Finance Minister Grant Robertson outlined the current financial supports in places for businesses.

The Leave Support Scheme, paid at the same rate as the wage subsidy, supports those not able to work because they have Covid-19, are isolating as a contact or are awaiting test results.

The Short Term Absence payment also supports employees waiting at home for test results.

Council of Trade Unions economic and policy director Craig Renney said a catch with these government's support schemes was that the employer had to apply for them.

"That creates real challenges because essentially employees are reliant upon their employers to start paperwork, to do some admin on their behalf, and when employers may well actually get zero benefit themselves," he said.

Renney said workers living week-to-week, who might struggle to negotiate leave agreements or receive thinner pay packets, will be most vulnerable in the coming weeks and months.

With a spate of mass absenteeism on the horizon, deputy prime minister Grant Robertson concedes it could be another difficult phase in the pandemic.

"It is, I accept, a very high degree of uncertainty for those businesses at the moment and that's why we're just urging businesses firstly to make sure their workers get boosted as quickly as possible. Secondly, to have those business continuity plans in place, and obviously we're working with the essential ones around the 'test to work' approach."

Robertson said the government was closely monitoring the economy as the country settled into the 'red' traffic light system, and has not ruled out introducing further targeting supports.