Where a restriction is genuinely required by applicable law, or by the employer's own insurance or lease, it meets the standard only where it is real, complied with, disclosed to staff, and its basis identified.
What it may not be is a pretextual blanket ban dressed up as a constraint. The employer must carry insurance that covers the dogs it admits, and may not admit dogs its own cover excludes; the answer to a narrow policy is a better policy, not a hidden ban.