A push by supermarket giant Coles to reshape Australia's free-range egg market through a dramatic reduction in space for hens has been dealt a blow, with two key animal welfare groups questioning whether the eggs are genuinely free range.

The new Coles standard, which the egg industry is spending millions of dollars to meet, allows for one square metre per hen. This is 10,000 hens per hectare, almost a seven-fold reduction in space from the voluntary guidelines of 1500 hens per hectare. As there is no legal standard, industry observers expect Woolworths and Aldi to follow Coles, leading to a supermarket-driven redefinition of free range.

But the RSPCA, which has applauded Coles for dumping its house brand cage eggs and endorses its barn-laid eggs, wants more scientific evidence that hens are not harmed by the ''dramatically increased'' stocking densities in its intensive free-range systems, with 30,000-hen sheds common.

The Coles standard, to be featured on egg cartons within weeks, allows for inside densities of 12 birds per square metre but every hen is within nine metres of an outdoor ''pop hole''.