20.—(1) This Article applies to any work for a person (“the principal”) which is available to be done by individuals (“contract workers”)—
(a)who are employed not by the principal himself but by another person, who supplies them under a contract made with the principal; and
(b)who, if they were instead employed by the principal to do that work, would be in his employment in Northern Ireland.
(2) It is unlawful for the principal, in relation to work to which this Article applies, to discriminate against a contract worker—
(a)in the terms on which he allows him to do that work; or
(b)by not allowing him to do it or continue to do it; or
(c)in the way he affords him access to benefits or by refusing or deliberately omitting to afford him access to them; or
(d)by subjecting him to any other detriment.
(3) Paragraph (2)(c) does not apply to benefits of any description if the principal is concerned with the provision (for payment or not) of benefits of that description to the public, or to a section of the public to which the contract worker in question belongs, unless that provision differs in a material respect from the provision of the benefits by the principal to his contract workers.