Rail commuters will find out on Tuesday how much the cost of season tickets will increase by next year, as trade unions warn that passengers are paying “more for less”.

The government links the annual January rise in Britain’s regulated fares with the previous July’s retail price index (RPI) measure of inflation, which will be announced by the Office for National Statistics (ONS) at 9.30am.

It is predicted to be about 3.5%, leading to the highest increase in fares in five years.

Regulated fares make up almost half of all tickets and include season tickets and standard returns.

Fewer than half (47%) of passengers are satisfied with the value for money of train tickets, according to the latest survey by passenger watchdog Transport Focus.

Successive governments have cut taxpayer funding of the railways and increased the relative contribution of passengers.

Rail unions said that, even as fares rise, rail engineering work is being delayed or cancelled, skilled jobs are being lost and staff are being cut on trains, stations and ticket offices.

They are calling for reduced fares, public ownership and protection of jobs during protests on Tuesday outside railway stations across the country, including in London, Birmingham, Cardiff, Bristol, Glasgow, Manchester and Liverpool.

The Transport Salaried Staffs Association leader, Manuel Cortes, said: “Dick Turpin had the decency to wear a mask when he robbed his passengers. Today train companies, with the government’s blessing, hide behind the retail price index as a method of legitimately fleecing more money from hard-pressed passengers at the start of each new year.”

Mick Whelan, general secretary of train drivers’ union Aslef, said: “After years of austerity, when workers have not achieved pay increases for years at or around inflation, it is unfair that the industry they subsidise creates transport poverty and hurts the communities and industries that they should be supporting.”

Examples of annual season tickets at current prices include: Brighton to London, £4,184; Liverpool to Manchester, £3,044; Worcester to Birmingham, £1,348; and Bath to Bristol, £1,580.

The chief executive of the Campaign for Better Transport, Stephen Joseph, called on the government to use the consumer price index (CPI) measure of inflation to set rail fares. CPI is generally lower than RPI and is used to calculate changes in benefits.

Joseph said: “This rise will be the highest since 2013, and will leave many commuters struggling to meet the cost of their commute next year.

“Passengers would be forgiven for thinking they are being taken for a ride when RPI has been dropped as an official measure for most other things.”

The ONS warned last month that RPI is “flawed” and has “serious shortcomings”.

The transport secretary, Chris Grayling, prompted outrage when he announced just before parliament went into summer recess that plans to electrify many rail routes had been cancelled or downgraded.