The Competition Authority is urging schools to allow a number of different retailers to sell school uniforms.
The authority said some schools still have a policy of appointing one exclusive retailer to sell uniforms.
It pointed out that competition between retailers tends to result in lower prices and better quality.
In May, the authority received a complaint from a retailer who wished to sell a school uniform for a school which had previously had one exclusive retailer.
However, the manufacturer refused to supply the uniform to them.
The Competition Authority intervened, and the manufacturer agreed to supply the complainant with the school uniform in question.