Care home staff are not receiving the money they are due from a special support fund, MSPs have been told.
Unison Scotland has written to the Scottish Parliament's Covid-19 Committee saying it is a "disgrace" the scheme is still not fully functional.
Health Secretary Jeane Freeman has said she will look into the issue, adding she cannot understand why employers would not accept the "free money".
The social care staff support fund was designed to protect the incomes of care workers if they fell ill with Covid-19 or had to self isolate.
In a written submission to the committee, the trade union said: "Poor staffing practices are still widespread in the sector - this means that large numbers of staff have no access to proper sick pay protections.
"This in turn meant that staff, if they either believed themselves to ill with Covid-19 or that they had been in contact with those who were, had the choice between taking a risk in going to work or feeding their families."
Unison said the problem is worst in privately operated care homes, with some companies claiming they cannot interpret the regulations so will not pay out.
Other employers are using a very narrow definition of the hours a staff member works, leaving them considerably out of pocket, the union says.
Its written submission states: "It is a disgrace that even now the scheme is in many cases still not fully functional - that this is the case is another sign that our care home system is not fit for purpose and needs radical reform."
At a meeting of the Covid-19 committee on Tuesday, Scottish Labour MSP Alex Rowley asked Freeman about the "significant failing".
He said: "Many employers are still denying staff the payments which make the difference between them having to risk their own and their clients' health."
She replied: "Where any of the unions or any other party has evidence of an employer who is continuing to pay only statutory sick pay and not accessing the fund, then we would want to know that and try to understand with the employer what it is that is stopping them.
"Because in essence this is free money, if you like, to the employer."
