Fares for some bus season tickets in Bristol and Somerset are to be cut for a fortnight.
Public transport operator First said the move was an attempt to boost the number of people using its services.
First Bus said the reduction was a "genuine attempt" to attract people on to the buses and keep them there.
"We'll take a view on numbers and demand. If we need to tailor it in slightly different way we will consider it," a spokesman said.
South West Transport Network, which campaigns on behalf of public transport passengers, said if the experiment worked it could boost the volume of passengers travelling.
"If we can get the numbers then the bus company could cut the fares," the spokesman added.