Disability advocacy group CCS says early childhood funding rules are short-changing disabled children.
The organisation says many disabled children cannot use their full entitlement to 20 hours a week of free, or near free, early childhood education because one-on-one support for them is capped at 15 hours.
The Education Ministry says there is no cap, but admits that of the 845 children getting support, only two get more than 15 hours a week.
CCS Disability Action chief executive David Matthews said the problem limited disabled children's access to education at a time when the Government was trying increase participation.
"Whilst we are trying to encourage participation of all young children in early childhood education, we're limiting that participation if a child happens to have a significant impairment that requires education support worker support."
Mr Matthews said another problem was that support worker funding did not cover school holidays, which was tough on families in which parents had to work during those holidays.
He said many families felt hard done by.
Canterbury mother Shannon Alker has two 3-and-a-half-year-old daughters, Lily and Abby. Lily has severe disabilities and requires an education support worker for every moment she is at kindy, while Abby does not.
Ms Alker said the gap between the 20 hour funding subsidy and the maximum of 15 hours for support workers was frustrating and disappointing.
"Clearly that's five hours short of the 20 hours a week that my daughter Abby is eligible for, so it creates an access barrier for Lily to attend an early childhood education centre for the 20 hours that an otherwise healthy, normal, for want of a better phrase, child has."
Shannon Alker said Lily and Abby were not yet in early education for many hours, but there should not be a barrier to increasing Lily's attendance.
"It's actually a form of discrimination," she said. "Lily's being discriminated against for access issues to education on the grounds of disability. It's not okay."
The Education Ministry's head of sector enablement and support, Katrina Casey, said there was no formal limit on the number of hours early childhood support workers could work with young children with special needs.
"For example, there is a total of nine children receiving 15 or more support worker hours from the ministry - two children are receiving 16 hours - and we expect that number to rise."
Ms Casey said children should be able to attend any early childhood service without discrimination.