Dedicated ticket sellers at rail stations in Sydney are soon to be a thing of the past.

As a growing number of commuters and transport users adopt the Opal smartcard, the state government is preparing to get rid of all dedicated sales staff.

Some stations will still have staff selling tickets at certain times. But these staff will be in general "customer service" positions, and not restricted to sitting behind ticket windows.

Rail, Tram & Bus Union NSW branch secretary Alex Claassens said he had confirmed the long-term plan to remove all dedicated sales staff with Sydney Trains.

"Another 70 ticket sellers will be gone early next year and the remainder will be phased out some time after that depending on the roll-out of the Opal card," Mr Claassens said.

"We just don't have an exact timeline on when the last lot will go, but they will be progressively let go at some point," he said.

Sydney Trains ticket sellers were paid a marginally higher rate than general customer service staff because they were handling money.

Sydney Trains has started to make sales positions redundant, and while staff have been offered the opportunity to shift to other jobs, not all of them have been successful.

Terry Missingham, who worked on the railways for about 37 years including 27 years as a ticket seller, accepted a voluntary redundancy in June.

"I understand technology and sometimes it does take a position away," Mr Missingham said.

But he said Transport Minister Gladys Berejiklian's policy of not selling the Opal card at rail stations but at separate retail outlets meant trained rail staff were not given a chance to help commuters with the new cards.

"Some of the staff could still have provided the service but they were never given an opportunity because the government decided the Opal should be at retail shops," he said.

Ms Berejiklian announced last week that machines allowing people to top-up their Opal cards would be rolled out at selected stations from next year.

Other machines will eventually allow people to also buy Opal cards from stations.

Asked about the intention to get rid of dedicated sales staff, Ms Berejiklian said: "As has been the case all around the world, the introduction of electronic ticketing means customers no longer need to queue up to buy a ticket ever again to use public transport.

"I'm pleased to see that queues at stations are much shorter, particularly on Monday mornings.

"I've always said we will be guided by our customers when it comes to improvements on public transport, and I want staff out from behind the window on the platform."

A Sydney Trains spokesman said there had been a 55 per cent drop in ticket sales at train stations after the roll-out of the Opal card.

There are as yet no Opal cards for concession holders, though the government has said a concession card should be available early next year.