Where a public authority seeks to coerce a person into compliance with an unlawful administrative act, that person can challenge the validity of the administrative act. This is called a collateral challenge.

The right to challenge the validity of an administrative act collaterally in response to threatened enforcement arises because the validity of the administrative act constitutes an essential pre-requisite to enforcement. An administrative act or order will be treated as invalid only if the right remedy is sought by the right person in the right proceedings. Where there is attempted criminal or civil enforcement, this may be opposed on the grounds that the official has acted beyond their powers. The courts will hardly ever refuse to allow the validity to be challenged.

Where a pension fund sought to enforce an amendment to its rules that increased the contribution of the employer municipality, the court in South African Local Authorities Pension Fund v Msunduzi Municipality allowed the municipality to challenge the validity of the amended pension fund rule because it had not been proved that the rule had been approved by the Registrar of Pension Funds as required by the Pensions Fund Act 1956.