The Scottish Renewables study found businesses in the industry predict full-time equivalent posts in Scotland will drop 16.9 per cent in the next 12 months.
Its Employment Trends and Business Confidence survey also asked respondents how they feel about the future of the renewables sector more generally over the coming year.
More than four in 10 (41 per cent) said they feel either quite or very negative, while the same number said they are “neutral” about the year ahead.
The organisation has called for action from the UK Government to address the issues and boost confidence in the sector.
Director of policy Jenny Hogan said: “These results show that changes to and closures of support schemes are having an impact on our members and on the numbers of employees within their businesses.
“The UK Government is rightly excited about the economic opportunities presented by the impacts of the global shift to low-carbon energy, but it’s really important we don’t forget about the jobs in our renewable energy sector today.
“Onshore wind and solar are the two cheapest forms of electricity, but ministers are refusing to allow them to access long term contracts for power, which will result in a marked slowdown in investment and a decrease in employment, as our survey has suggested.
“For Scotland’s renewable energy industry to continue providing jobs and ever-greater reductions in carbon emissions, Government must act quickly to give companies the confidence they need to keep investing in our sector.”
The survey also found more respondents feel positive about the future of their own businesses over the next 12 months than negative.
Almost half (47 per cent) said they are either very positive or quite positive, while 32% are either very negative or quite negative.
Around a fifth said they feel neutral.
The SurveyMonkey poll was completed by 46 companies within the Scottish Renewables membership between 6 and 19 February.
WWF Scotland director Lang Banks said: “These are worrying findings and underline the urgent need for the UK Government to clarify its plans to support renewables and the thousands of people now employed in the sector.
“Scotland has incredible natural renewable energy resources, but if it is to maximise the economic opportunities on offer, the UK Government must provide energy companies with a clear route to market.
“However, given we’re part of the GB energy market, this is not just an issue for Scotland. As a net exporter of electricity, Scotland plays a key role in helping the whole of the UK in cutting its carbon emissions.
“If we are to be able to plug in to the cheapest and cleanest forms of power generation then it’s vital our political leaders north and south of the border do all they can to support renewables.”