First Minister Nicola Sturgeon is set to announce whether the toughest Covid restrictions will be imposed in the west of Scotland.
She said on Monday that it was “likely” but not inevitable that some areas would be moved into level four.
Concerns have been raised about “stubbornly high” rates of infection in Glasgow and many surrounding areas.
No part of Scotland has been placed in level four since the new tiered system came into effect.
However, there have been fears that infection levels are not reducing quickly enough in Lanarkshire and the Greater Glasgow and Clyde health board area, with the possible exception of Inverclyde.
More than 1.75 million people live in the areas which have been warned they could face tougher measures.
Level four restrictions would see the closure of a wide range of premises including non-essential shops, pubs, restaurants, hairdressers, barbers, gyms and leisure centres.
Ms Sturgeon said moving to the highest level “for a limited period in some areas” could help protect the NHS and pave the way for some easing of restrictions at Christmas.
Level four is the closest to a full lockdown, similar to the one introduced in March.
Socialising would not be allowed in people’s homes, but six people from two households could still meet outdoors and there would be no limit on outdoor exercise.
However, people would be advised to minimise the number of meetings with people from other households, and to follow social distancing guidance.
Those living under level four restrictions would be advised to avoid any unnecessary travel out of the area, and to keep journeys within the area to an absolute minimum.
The premises which would close include:
However, schools would remain open full-time.
The Scottish Retail Consortium has warned of the impact such a move would have on shops.
Director David Lonsdale said: “The scientific evidence indicates retail is a safe environment and closing stores will do little to suppress the virus.
“However, the economic impacts of forced closure during the Christmas trading period are severe, which is why it should only be a last resort.”
The new five-tier system – which ranges from level zero to level four – came into force on 2 November, and is reviewed on a weekly basis.
At present 22 of the 32 council areas in Scotland are under level three. Aberdeen, Aberdeenshire, Argyll and Bute, Borders, and Dumfries and Galloway are in level two, with Highland, Moray, Orkney, Shetland and the Western Isles in level one.
Ms Sturgeon’s cabinet will decide on any changes on Tuesday morning before she makes a statement in the Scottish Parliament in the afternoon. Any new measures will take effect from Friday.
Talks have been taking place between the Scottish government and the local authorities in the areas which are under threat of being placed into level four.
Deputy First Minister John Swinney said on Friday that councils in the west of Scotland had been warned that such a move was possible.
On Monday, Ms Sturgeon said: “I think it is likely that we will see some areas go to level four this week.
“But is it inevitable? Until we have taken that final decision, no of course it’s not.”
The first minister added that the government was also looking at whether any areas could go down a level, saying: “This is not a one-way street.”