Fare rises of almost 11% await some train commuters when they return to work on Tuesday after the Christmas break, rail customer watchdog Passenger Focus said.
The annual rise will mean regulated fares, which include season tickets, going up by an average of 6%.
But Passenger Focus highlighted higher-than-average rises on some routes, including Chester-Crewe where the annual season ticket is going up 10.6% compared with the January 2011 price.
There is also a 10.6% rise for season ticket holders travelling between Llandudno and Bangor in Gwynedd, while a Port Talbot Parkway-Swansea season ticket goes up 8.7%.
Some London commuters will also have to fork out for above-average increases, with a season ticket between Northampton and the capital rising 6.9% to £4,756.
The average rise today for all rail tickets, including ones that are unregulated and which can be raised to any level, is 5.9%.
Passenger Focus picked out rises of above 9% for some off-peak returns compared with the prices passengers were paying in January 2011. For instance a London-Cardiff off-peak return rises 9.7%, with London-Exeter going up 9.6% and London-Plymouth also increasing by 9.6%. Anytime-return fare rises that are well above average include Birmingham-Edinburgh (up 8.4% compared with January 2011) and Bristol-Edinburgh (up 8.3%).
However, Passenger Focus said it felt that unregulated fares had "not been hit in the same way as in previous years" and that it hoped this policy continued. Passenger Focus chief executive Anthony Smith said: "Passengers will have to dig deep in their pockets to cover the 6%-and-more fare rises coming into effect on Monday. Whatever the weather, these rail fare rises will make for a frosty return to work."
Michael Roberts, chief executive of the Association of Train Operating Companies, said: "Money raised through fares helps to pay for better services. For a number of years, the Government has sought to sustain investment in the railways by reducing what taxpayers contribute and increasing the share that is paid for by passengers.
"The focus of the whole industry is to keep on reducing the overall cost of running the railways as a way of limiting future fare rises and providing taxpayers with better value for money."