Professor Cathy Nutbrown of Sheffield University says the government has rejected most of the recommendations in her government-commissioned review of early years education.
Prospect Deputy General Secretary Leslie Manasseh said: "Our members in early years settings agree with Nutbrown's warning that the youngest, most vulnerable children will suffer if there are too few adults for too many children, no matter how well qualified the adults happen to be.
"This raises questions not only around the wasted cost of this consultation, but also why the Government has chosen to ignore the findings of the expert they appointed.
"Our message to Elizabeth Truss is that the government must listen to the professional experts on the ground, and think again about its plans to increase staff-child ratios – from 1:3 to 1:4 for one-year-olds and under in nurseries; 1:4 to 1:6 for two to three-year olds in nurseries; and from 1:8 to 1:13 for the three-plus age group in nurseries – by September this year.
"The government claims it will consult, and that means listening to the professionals expected to deliver, who are our members. Instead, it is once more trying to do things on the cheap, putting professionals in an impossible position and children at risk."
The Aspect Group of Prospect represents 3,000 advisory head teachers, directors and managers of children's services, school improvement and early years advisers, education welfare officers, 14-19 coordinators, heads of Sure Start, Ofsted inspectors, parent partnership staff and self-employed consultants.