Pressure is building on the NSW government to use the tens of millions of dollars it collects each year from train passengers passing through stations at Sydney Airport to cut the cost of the trip there, the most expensive on the city's rail network.

The latest accounts filed with the corporate regulator for the private operator of the four stations on the nine-kilometre Airport Line tunnel show it paid the government almost $87 million in a "train service fee" in the year to June, a 26 per cent rise on the same period a year earlier.

A one-way journey between Sydney's CBD and the domestic and international terminals costs an adult passenger $18.10 during peak hours. Of that single-trip fare, $13.80 is for a station access fee.

The access fee – which rose by 3 per cent last year – does not count towards the daily travel cap for holders of Opal cards.