EasyJet objected to a Go ad in the national press promoting a £65 return fare including taxes to Nice for the forthcoming Monaco Grand Prix.
The ASA agreed that the claim was inaccurate because the low-cost fare applied only to certain dates and that passengers would have to set aside a total of six days to benefit from the offer.
easyJet also complained about a Go claim that its highest fare was more than "40% less than easyJet". The ASA said it was "unlikely" readers would realise that this was only when both airlines' top prices were compared.
The ASA told Go to ensure that all future ads clarified the restrictions on dates of travel for the prices quoted.
A spokesman for Go said it was disappointed that the ASA believed that customers could be confused by the wording in this case. "However, the key fact in the advertisement is not in question -- on easyJet, the highest fare to Nice is 40% higher than the maximum fare on Go," he added.