People are being asked to go back to working from home from today, unless it's necessary.
It's a complete reversal of the rules that were relaxed in September.
But the Government's being warned it may not have the desired effect on Covid-19 case numbers.
Neil McDonnell, Chief Executive of ISME, says the economy could be damaged for little benefit.
"There is a degree of frustration on our part that the epidemiological data that was out in November giving details of transmission do not suggest that the workplace.is a significant vector for transmission.
"The danger is we could shut down offices without substantially improving the caseload."
