21. It is unlawful for a person who is empowered by virtue of a statutory provision to select or nominate another person for employment by a third person to discriminate against a person, in relation to employment in Northern Ireland,—
(a)by refusing or deliberately omitting to select or nominate him for employment; or
(b)where candidates are selected or nominated in order of preference, by selecting or nominating him lower in order than any other who is selected or nominated.