Primary schools have been told not to assist companies which promote their goods by using pupils in special promotions.
The Irish Primary Principals' Network (IPPN) said schools should reject promotions that involve children encouraging their parents to buy certain products in a particular store.
Companies in recent years have become heavily involved in promotions where, if a child or its parent collects tokens or vouchers, the local school can acquire expensive equipment or computers.
The IPPN said schools should not facilitate outside agencies or commercial bodies to promote their products and services through children.
It added: "The collection of stickers, tokens and vouchers as a prerequisite to entering competitions (with sometimes dubiously attractive prizes) is frequently nothing more than another form of sales promotion and marketing".
The IPPN said it was responding to requests for guidance from principals all over the State.
It said promotions which put pressure on pupils and parents had increased inordinately in recent years, and many schools had been flooded with material from companies and other organisations.
The issue of marketing and advertising has started to crop up more often in schools in recent years. Some companies now place advertisements on the walls of some second-level schools, although this has been criticised by some teachers.
The IPPN said, however: "Many schools have established very effective local partnerships with shops and businesses which can be professionally and ethically acceptable and beneficial to a school but which do not require children to encourage their parents to buy products in a particular store."
The IPPN said schools were also concerned at the number of requests they received from charities for support. It said schools wanted to support good causes, but they should choose a small number and support them on a formal basis. Charities should be selected based on a ballot of teachers and pupils.