Face coverings will also be a legal requirement in customer-facing areas of some States public buildings.
Masks will have to be worn in communal areas of schools, but not in businesses where it would effectively prevent them from operating.
In practice, this means that gyms, restaurants, pubs and nightclubs can continue to operate, and office Christmas parties can still legally go-ahead.
As well as tightening up the rules on masks, the CCA has agreed new travel restrictions.
From Wednesday, all fully vaccinated travellers who have been to a non-Common Travel Area country will need to do a PCR test on arrival and isolate until they get a negative result.
All arrivals who have only been to the Common Travel Area will have to buy lateral flow tests, costing £25, and complete the course of tests over 10 days.
So far, Guernsey's on-island sequencing has not detected any cases of the omicron variant as all recent cases sequenced have been the Delta variant.
Further changes to the rules means that anyone who is identified as a close contact of a confirmed or suspected case of the Omicron variant will have to self-isolate, regardless of their vaccination status or age.
These contacts will be notified by Public Health and told to self-isolate for 10 days, or until the case they were in contact with is confirmed to be of the Delta variant, or another lineage.
Deputy Peter Ferbrache, the chairman of the CCA, said it had to recognise the uncertainty that the Omicron variant brings.
'The measures that we are introducing are precautionary and reflect the uncertainty of the current situation.
'It may be a greater risk than the Delta or other variants, and it may not, and so we are quickly stepping both our border and local rules as a precaution.
'But we’re not seeking to overreact, either and we want people to continue to be able to live, work, attend school and enjoy the festive period with as little unnecessary disruption as possible, mindful that we do have a highly vaccinated community and this is not a repeat of what we faced when the very first cases of Covid-19 were emerging around the world.
'We do need more information on the efficacy of vaccines against the new variant, but we’re also advised that the
vaccines we have administered will offer some protection.
'That means we must work quickly to continue our booster programme and encouraging anyone who has not yet been vaccinated to do so.'
The CCA briefing is streamed live via gov.gg and on the States' Facebook page at 6pm.
Full details in tomorrow;'s Guernsey Press.