The Government should rule out possible plans that could see even higher fares for people travelling by train at the heart of the rush hour, a report by MPs said.
Ministers should also set out a long-term policy on annual season ticket fare rises, the report by the House of Commons Transport Committee says.
Reducing the cost of the railways to taxpayers must not be achieved by "ramping up fares", said committee chair Louise Ellman.
She added that it was vital that the public knew more about how public money was spent on the railways "so that there is confidence it does not leak out of the system in the form of unjustified profits".
The committee's report on the railways comes just two days after inflation-busting average rises of 4.2% for regulated fares, which include season tickets, took effect for passengers.
Following Sir Roy McNulty's report into rail costs, the Government is currently looking at a variety of measures. These include possibly managing peak-time demand by increasing fares for those wanting to travel when the rush hour is at its height.
The committee's report said: "We recommend that the Government rule out forms of demand management which would lead to even higher fares for commuters on peak-time trains". The report continued: "Higher prices at peak times might make a difference to demand at the margin but would for the most part be a tax on commuters who have no effective choice over how or when they travel."
This year's regulated fare rise would have been even higher had the Government not pulled back from the original plan of an RPI plus 3% rise in favour of a formula which limited the increase to RPI plus 1%. The committee said it welcomed the decision not to proceed with RPI plus 3% but MPs were "concerned about where that leaves the Government's fares policy, especially at a time when it is attempting to reduce the cost of rail to the taxpayer".
The committee said it was "very concerned" about the safety implications of proposals to reduce staffing at stations and on trains. Also, MPs said rail regulators should ensure high standards of rail safety were "not jeopardised by different ways of working between Network Rail and train operators". In addition, the committee called for the setting up of a "strong, single economic regulator for the rail industry" to deliver savings across the board.
Bob Crow, general secretary of the RMT transport union, said: "While this report reinforces once again that our railways are nothing more than a multibillion-pound rip-off lining the pockets of a bunch of spivs and speculators, it ducks the real issue and that's the cast-iron case for public ownership. You can't have transparency, accountability and value for money while our railways are bust apart and run as a money-making racket for a gang of private operators."