John Miller Law solicitor Maria Bagnall said the new stance was "too restrictive" and meant some women may be missing out on cover they should be entitled to.
"We're worried that they won't even think of challenging ACC, when it puts this policy out saying they're not going to cover these types of injuries," Bagnall said.
"There are many scenarios where women can make a treatment injury claim and it's an incredibly complex area of law. What needs to be looked at are the merits of the case, not a policy that ACC put out."
ACC said its new guidance was formulated by a panel of experts including obstetricians, midwives and academics, and was issued after finding inconsistencies in how claims were being made between DHBs. A literature review on research into tears was also carried out as part of its decision.
Another ACC law specialist, Phil Schmidt, believed the agency's stance was based on an interpretation of a 2017 Court of Appeal ruling it won on treatment injuries.
"ACC have interpreted this Court of Appeal decision to mean all treatment injuries must be failure-based. That largely makes the treatment injury regime pointless."
That was because a law change in 2005 was made to remove the need to prove failure, he said.
"But the way they're interpreting the court's decision is that you do need to prove failure and there's really no point. In my view ACC's approach to the treatment injury concept has really returned us back to the bad old days."
This interpretation was also impacting the way other injuries claims were being treated by ACC and it should be challenged in the courts, but that was difficult and expensive to do, Schmidt said.
In statement, ACC chief clinical officer Dr John Robson said the organisation "acknowledges that there are some women who face severe and life-changing physical and mental challenges as a result of perineal tears whether or not they are eligible for ACC cover".
"We don't wish to diminish their experience. We understand and appreciate they have severe lifelong complications," Robson said.
"ACC has recently provided clarification on cover issues for treatment injury perineal tears. This was done in consultation with experts in the sector including obstetricians, academics and midwives and has provided increased certainty for treatment providers.
"ACC considers each case based on its own evidence and in light of the legislation. Cover will be available for a treatment injury if a tear has been caused by treatment, or a failure to provide appropriate treatment."
ACC had revoked the perineal tear claims of two women since 2005 but it did not plan to retrospectively review all accepted claims as a result of last year's clarification, he said.
