'Almost 85,000' workers on zero-hours contracts in Scotland
As many as 85,000 people in Scotland could be employed on zero-hours contracts, according to the Scottish Trades Union Council.
Under the contracts, employees agree to be available for work as and when it is required, with no guarantee.
General secretary Grahame Smith said the issue had been ignored for too long and was a form of "bonded labour".
The STUC said its interpretation was the first time a breakdown of figures had been estimated for Scotland.
Mr Smith said: "Zero-hours contracts and insecure employment contracts are all that's on offer for a significant amount of workers.
"They don't have the choice of whether or not they have a zero-hours contract, that's what they are given by the employer, and that's unacceptable and it's a form of bonded labour.
"They are in effect tied to that employer waiting at the whim of the employer to know whether or not they are going to be working, how many hours they are going to be working and of course what income they are going to derive from that work.
"And that's just something which is totally unacceptable."
The STUC said it had not been aware of any official attempts to estimate the figure for Scotland, so it looked at the available data.
It based its calculation on a Chartered Institute of Personnel and Development (CIPD) survey of 1,000 employers from August 2013, which concluded that about one million workers in the UK could be employed on zero-hours contracts.
Recent Office of National Statistics figures put the estimate much lower at 583,000 UK contracts, but the STUC said this was a "significant under-estimate".
The organisation said it was not consistent with its workplace intelligence and the survey results were "unreliable" due to sampling and reporting error.
It concluded: "The STUC believes the CIPD estimate is more accurate.
"If there are one million people employed on zero-hours across the UK it would be reasonable to assume that approximately 84,800 people in Scotland are currently employed on zero-hours contracts."