Most temporary workers in Scotland's public sector lag behind full-time colleagues in terms of wages,sickness and holiday pay, according to a survey.
Scotland's temporary workers feel they are losing out on pay
The Unison survey found that workers felt trapped in low-paid jobs with little chance of career progression.
The union has published a booklet designed to advise workers on their rights.
Dave Watson, of Unison Scotland, said one female worker had been in temporary posts for 38 years.
The union said there had been a huge rise in the number of temporary staff in the past 10 years and they had problems obtaining credit and mortgages.
Mr Watson said: "Whilst there has been some improvements in the legal lot of temporary workers, this survey shows that much more could be done.
"Many women have been trapped on the temporary contract merry-go-round for 20 to 30 years.
"We even found one woman who had been in temporary posts for 38 years.
"That is why we want employers to take their responsibilities seriously, implement the new legislation properly and stop abusing temporary contracts."
Unison highlighted the case of museum worker Lynsey Johnston, from Glasgow, who was a member of temporary staff for four years.
It said Ms Johnston and other temporary colleagues had their full-time posts scrapped following a review.
She explained: "Temporary staff were not considered by a recent best value review, even though we were doing the same jobs as permanent staff.
"We ended up having to apply for part-time jobs and many of my colleagues couldn't afford the wage loss."
Mr Watson added: "The problem has been growing for some time and it is time that both employers and trade unions addressed the problems.
"We have produced this booklet both to outline the scope of the problem and to give solid advice to our activists on the legislation to use."