About 75% of all the trains that run between Par and Newquay in Cornwall are to be cut under new plans.
The Strategic Rail Authority (SRA) is to cut the eight trains which currently run on the branch line every day.
From April next year, the trains will be replaced with a new daily London Paddington to Newquay service and one Par to Newquay train.
Rail users in the county said they are furious and are planning to fight the proposals that have been put forward.
The SRA said it is reducing the service because of low demand, but rail users in Cornwall said they are angry and dismayed.
There are plans to form an action group to fight the SRA's proposals and people are being urged to write to the authority with their objections before the end of the month.