The expanded strike would stop the movement of coal exports valued at about $50 million over the two days.

Pacific National spokeswoman Marie Festa insisted the parties were still involved in "productive negotiations" but Rail, Tram and Bus Union organiser Steve Wright said the strike was all but certain to go ahead.

Mr Wright said industrial action had gone from the 24 hours revealed in yesterday's Herald to 48 hours and had spread from the Hunter Valley to coal lines to across NSW.

"All up, we expect more than 500 drivers and other staff from Port Waratah, Muswellbrook, Antiene, Mudgee, Port Kembla and Lithgow to take part in the action," Mr Wright said last night.

He said the union wanted pay rises of 15 per cent over three years for its members, and while Pacific National had lifted its offer to match the union's in "nominal terms", the pay offer was dependent on the coal operations coming in "7 per cent under budget, which is something we have no control over".

He said a hearing in the Fair Work Australia tribunal in Sydney yesterday extended the union's right to take legal strike action beyond a deadline due to expire on Friday.

He said striking Pacific National workers would set up "peaceful" pickets at the various company depots and he expected the company would try to put strike-breaking drivers on trains.

Ms Festa said the company was "optimistic" the strike could be averted with talks today.

She described today as "D Day" for the strike talks.

Pacific National is the largest rail hauler in the NSW coal industry. It is owned by Asciano. It runs 27 trains in the Hunter and has an estimated 80 per cent or more of the state's coal haulage market. Mr Wright said the strike would not affect operations by Queensland Rail.