The survey also found that 62% of nurseries faced "significant challenges" in retaining staff.

Children's Minister Maree Todd said the survey represented less than a quarter of private sector nurseries.

And she added that local authority funding to private providers had increased significantly.

From August next year, eligible children will be entitled to 1,140 hours of free pre-school education.

'Grim picture'

The NDNA has said it is worried that private and third sector nurseries are facing a "staffing crisis" ahead of the major policy change.

Purnima Tanuku, the NDNA chief executive, said: "The results of our research paint a grim picture, with 71% of employers telling us they have problems recruiting staff at practitioner level.

"A further 62% have significant challenges retaining their existing staff who are leaving for higher salaries in schools and council-run nurseries.

"On the funding rates partner providers get from councils, they cannot hope to compete with the salaries on offer for the same roles.

"Working parents value the flexibility that private and third sector nurseries, open all year round, can give them. This choice must not be compromised."

The NDNA survey found that annual staff turnover rates were at an average of 29% of the entire childcare staff employed by providers.

Moving to the public sector was the most common reason given by those leaving private nurseries.

From August 2020, every parent in Scotland will be entitled to 1,140 hours of free childcare for all youngsters aged three or four, as well as eligible two-year-olds, up from the previous entitlement of 600 hours.

Concerns have been raised over the implementation of the 2020 plan but the Scottish government insisted they were on track.

Increased training opportunities

Scottish Labour education spokesman Iain Gray MSP said: "SNP ministers have been told again and again that the workforce is not going to be in place to deliver their flagship childcare policy.

"This is yet another wake-up call.

"They need to start listening before families across Scotland are let down."

Children's Minister Maree Todd said: "This survey represents less than a quarter of private sector nurseries.

"We have increased training opportunities and routes into the sector, alongside our recruitment campaigns, and enabled providers to advertise for free on the campaign site.

"As a result, there are more people than ever before working in early learning and childcare, with a 40,000-strong workforce."

She added: "Local authority funding to private providers has also increased significantly, with rates increasing by 26% over the two years to this August and further increases expected from the implementation of 1,140 hours next year.

"Private providers deliver high-quality early learning and childcare and we will continue to invest to support expansion and work with the sector, including the NDNA."