The NSW government knew it would face a driver shortage and warned of 18 peak hour cancellations due to "excess leave approvals" ahead of Sydney's train chaos, the public transport union claims.
The revelation by Rail, Tram and Bus Union divisional secretary Robert Hayden comes after the system melted down this week leaving thousands of frustrated passengers stranded on platforms across the city.
Rail bosses blamed driver sickness and lightning strikes for the problems which peaked on Tuesday.
But in a letter to Sydney Trains chief executive Howard Collins, Mr Hayden on Monday said the government was aware it would face issues and had shared its concerns with union representatives on Friday.
"We were specifically told: That owing to a driver shortage brought about by 'excess leave approvals' there will be service impacts on Monday 8th, Tuesday 9th and Monday 15th of January," the union boss wrote.
Mr Hayden said the government had unfairly vilified train drivers by blaming them for the network meltdown.
"To falsely attribute blame to train drivers may leave our members exposed to criticism, ridicule and possible attack at the hands of Sydney commuters," he wrote.
"Gaps in driver coverage are a result of a failure to recruit enough drivers in advance of the new timetables."
Transport Minister Andrew Constance admits he's worried about how the system will cope next week.
"We have one tough day next Monday," he told 2GB Radio on Thursday morning, citing annual leave issues and the new Hornsby junction scheduled to come into operation.
Mr Constance expects a meeting will take place on Thursday between Sydney Trains and the union.
Thursday's proposed meeting comes ahead of upcoming union pay negotiations but Mr Constance says he has "no evidence" the spike in sick leave this week was a guerilla tactic being used to strongarm the government.
He did insist, however, he would "stare down" the union and would not budge from a government cap of 2.25 per cent on salary increases - well below the six per cent being sought.
"We're happy to give an increase above inflation at the moment, with the wage cap, but six per cent per annum that's off the charts," the minister said.
Mr Constance on Wednesday ordered a review of Sydney's new timetable be handed to him within a fortnight.