Rail fares have increased twice as much as pay since 2010, according to new research.
The findings have been revealed ahead of the announcement on how much prices will go up next year.
Commuters will find out how extra they will be charged from the new year on Tuesday (August 15), and a dramatic increase is expected.
In 2016, the rise in fares - which is linked to the previous July's Retail Price Index (RPI), - was 1.9%.
Now, this year's figure is expected to be around 3.9%, which would lead to the highest increase in fares since 2012.
While average weekly earnings have grown by only 16% in eight years, an analysis by the Rail, Maritime and Transport union (RMT) showed that rail fares have risen by around 32%.
The rise means for example, a new nurse or police officer commuting from Chelmsford to London, where an annual season ticket would cost £4,000 after the latest rise, would pay 20% of their salary on an annual season ticket, claimed the union.
RMT general secretary, Mick Cash said: "Government policy of suppressing workers' wages while at the same time presiding over corporate welfare on our privatised railway has resulted in a toxic combination of fare rises easily outstripping wages."
The private operators and government say the rises are necessary to fund investment.
However, they are pocketing the profits while passengers are paying more for less, with rail engineering work being delayed or cancelled, skilled railway jobs being lost and staff cut on trains, stations and at ticket offices.
A Department for Transport spokesman said: "The Government carefully monitors how rail fares and average earnings change, and keeps under review the way fare levels are calculated.
"We are investing in the biggest rail modernisation programme for over a century to improve services for passengers - providing faster and better trains with more seats.
"We have always fairly balanced the cost of this investment between the taxpayer and the passenger.
"We are driving the industry hard to improve efficiency to ensure we maximise the value of passengers' and taxpayers' investment in the railways.
"Regulated rail fares are capped in line with inflation for next year."
Paul Plummer, chief executive of the Rail Delivery Group, said: "Money from fares pays to run and improve the railway, making journeys better, boosting the economy, creating skilled jobs and supporting communities across Britain, and politicians set increases to season tickets.
"It's also the case that many major rail industry costs rise directly in line with RPI.
"Rail companies are working together to improve performance now, adding thousands more seats over the next 18 months and, longer term, simplifying fares and ticket buying so that the country has the railway it needs to prosper."
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