This follows an incident in which two youths claim they were assaulted and falsely imprisoned by a group of Newham park constables.
Their lawyer Simon Smith said: 'I have approached the Legal Aid Board for [funding]. This case is a matter of public interest because it raises issues for local government.
'If you grab people and put them in a van it is a matter of assault and false imprisonment.'
Newham set up a parks constabulary to enforce by-laws to tackle anti-social behaviour.
Its interim service head Trevor Kennett was last month appointed a Home Office adviser.
A Newham spokeswoman said parks constables' powers were defined in section 24a of the Police and Criminal Evidence Act 1984.
This covers the powers of people other than police to make what are commonly known as citizen's arrests.
She confirmed an internal investigation is taking place.
A council investigation last winter found several controversies involving the constables, which included some
carrying police-style batons.