The warning comes after Nicola Sturgeon said the measure was under “active consideration” in a Covid update to MSPs on Tuesday.
The self-isolation requirement will be removed for all adults who have had two vaccine doses from August 9, but this may be brought forward for healthcare staff, amid staff shortages in health boards across Scotland caused by self-isolation.
But some unions have warned against this.
The GMB said it would cause “anger and concern” among staff, and the Royal College of Nursing (RCN) said the Scottish Government must provide evidence the measure could be done safely.
Martin MacGregor, vice-chair of the RCN Scotland Board, said non-urgent remobilisation should be scaled back to reduce short staffing, ahead of any move to change isolation requirements.
He said: “Our members remain under pressure at the moment as hospital and ITU numbers are rising while a significant number of staff in health and social care are required to self-isolate.
“It is essential that nursing staff are able to work safely, wherever they are employed, and the RCN cannot support the current proposals from the Scottish Government to allow the early return of self-isolating staff.
"The Scottish Government needs to set out the evidence demonstrating that Test and Release can be done safely. The RCN expects that re-mobilisation plans should be limited as the first measure to increase capacity.
"Employers should also be making sure that nursing staff have access to the highest level of PPE.
“As the First Minister acknowledged yesterday, to relax the rules for one group of people could be seen as giving health and care staff less protection than the wider public.”
The GMB union warned the First Minister to “not go there”.
Senior organiser for public services Drew Duffy said: “Our message to the First Minister is simple – ‘don’t go there’. This will only anger and concern staff who are already absolutely exhausted and undercut, while confirming that their safety is not and has never been a priority for this government during this Covid-19 pandemic.
“Instead, this should act as a final warning about the need for urgent and transformative investment in health and social care, so we can attract and retain the people and skills we so obviously need, and that means delivering proper value for workers in their pay and conditions.”
In response to a question from Liberal Democrat MSP on Tuesday, Ms Sturgeon said a change for healthcare staff was under “active consideration”, but the Scottish Government would listen to the views of unions.
She said: “I am very mindful of the fact that when I talk about this … as something that would help to keep key essential services going, the people who work in those services might hear it differently.
"They might hear it as us giving less protection to their health and wellbeing, so we need to be as careful and cautious about that as we are about everything else.”