You can file a defence against a notice that is not mandatory (see Annex A) and you can challenge the validity of the notice whichever process has been used.
Gallwch gofnodi amddiffyniad rhag hysbysiad nad yw'n orfodol (gweler Atodiad A) a gallwch herio dilysrwydd yr hysbysiad ni waeth ba broses sydd wedi'i defnyddio.