Local authorities claim that some of their social services clients will miss out on the flotation because the Halifax insists that anyone with a mental disability should have an authorised signatory and will only pay out the share windfall - expected to exceed£1,000 each - to that nominee. Two councils are considering legal action.
The problem is that signatories - typically a social services team leader in a residential centre - often sign for several clients but are only eligible for one pay-out, which then has to be divided among the clients.
Cheshire CC claims that 50 elderly people with mental disabilities in its care will miss out because of the rule.
Cheshire says it will consider helping with a joint legal action if asked to by disability organisations.
Solihull MBC has 36 people with learning disabilities who hold accounts with the Halifax. Social services chairman Hugh Hendry said the council's social services director, Michael Hake, had raised the problem with the chairman of the Halifax, but to no avail.
Solihull members have asked Mr Hake to seek legal advice.
A statement from the Halifax said: 'Our lawyers have considered the Disability Discrimination Act. We have a very firm legal opinion that our scheme does not contravene this act.
'The Halifax does not discriminate against any group in society and certainly not the disabled. Many disabled people are members of the Halifax and will receive free shares. Those disabled who are beneficiaries of trustee accounts are in no different position from beneficiaries of other trustee accounts.'