Under Article 22 of European Regulation (EC) 1008/2008 on common rules for the operation of air services in the Community, airlines have pricing freedom in relation to air fares and air rates for intra-Community air services. This means that airlines are not only free to set their own pricing for air fares but also for any supplementary services, for example for baggage. Article 22 also requires that passengers booking a flight must be aware of final price of a flight including any supplemental elements selected by the passenger, at all times during the booking process.
If advertised prices are incorrect or misleading, this could be a breach of relevant consumer protection laws. The Competition and Consumer Protection Commission offer general advice on consumer affairs queries relating to advertised pricing.