The number of people being appointed to permanent jobs has fallen for the first time this year.
A new report showed a fall in recruitment to these positions in July.
The latest Bank of Scotland Report on Jobs found almost a third of recruitment agencies (31%) reported a drop in candidates placed in permanent posts, with this being linked to weaker economic conditions.
Meanwhile, just over a quarter of Scottish recruitment agencies (26%) reported a rise in the number of people finding permanent jobs.
Demand for both permanent and temporary staff increased at a weaker rate in July, while average salaries for permanent positions fell for the second month in a row — with the rate of decline for this the fastest for 22 months.
Donald MacRae, chief economist at the Bank of Scotland, said: "The Scottish labour market showed a marginal improvement in July but is losing momentum.
"The number of people appointed to permanent jobs declined for the first time this year, showing the effect of the current slowdown in the economy.
"However, the number of vacancies continued to increase, giving hope that the upwards trend in employment can be maintained."
The report is based on the experiences of more than 100 recrutiment and employment consultancies in Scotland.
For July it found five sectors — IT and computing, hotel and catering, nursing/medical/care, engineering and construction, and secretarial and clerical — saw an increase in permanent job vacancies.
The number of available permanent positions in the executive and professional sector, accounts and financial and the blue collar sector fell at a "solid pace".
For the first two of these three sectors, the rate of decline was the strongest for almost three years.
However, there was an increase in the number of people finding temporary work last month.
Approximately 45% of agencies placed a larger number of candidates in temporary positions in July, compared to 21% of agencies who reported a decline.
Demand for temporary staff increased in six of the eight employment sectors in Scotland, with secretarial and clerical seeing the fastest rate of growth in vacancies, closely followed by IT and computing.
But the nursing/medical/care sector, as well as the accounts and financial industry, saw the first reduction in temporary vacancies for 23 months.
A Scottish Government spokesperson said: "The Bank of Scotland Labour Market Barometer suggests there's been improvement in Scottish labour market conditions for the twenty-first month in a row, but that the rate of improvement is slowing.
"Last week's labour market statistics showed that Scotland has a higher employment rate than the UK as a whole — for the twenty-first consecutive month of labour market statistics — a lower unemployment rate, and a lower rate of economic inactivity compared to the UK-wide position. Scottish unemployment fell for the fifth consecutive months of statistics.
"The Scottish Government are doing all we can within our current powers to strengthen the economy, to create and bring jobs to Scotland, to stimulate growth, and to create the most supportive environment for business in the UK — and we are achieving results in terms of youth training, inward investment, and help for the small business sector.
"But it is clear that much more could be achieved, and the UK Government's repeated failure to give the green light to much needed capital investment is hampering progress.
"We need stimulus to capital investment by the UK Government to boost the construction sector and wider economy. Scottish GDP would have grown in the first quarter of the year if not for the problems that this hugely important sector faces — and that is why we have called on the Chancellor to invest an extra £5bn in capital projects, including the 'shovel ready' projects that we have identified in Scotland."