The NSW government knew it would face a driver shortage and warned of 18 peak hour cancellations due to "excess leave approvals" before Sydney's train chaos, the public transport union claims.
Transport Minister Andrew Constance also fears more problems next week.
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.
Mr Hayden accused the government of unfairly vilifying train drivers by blaming them for the network meltdown.
Rail bosses and the government had blamed driver sickness and lightning 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.
"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."
Mr 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.
The union says the meeting is long overdue and has welcomed the chance to help get the train system "back on track".
"It's incredibly disappointing that it's taken it to get to breaking point before management finally decided they needed to meet with the people who actually know how our transport system works, but we're glad that it has finally happened," NSW secretary Alex Claassens said in a statement.
Thursday's proposed meeting comes before upcoming union pay negotiations but Mr Constance says he has no evidence the 70 drivers who called in sick 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.
NSW Opposition Leader Luke Foley has called on Mr Constance to "come clean" about any planned cancellations scheduled for Monday.
"The minister's arguments that these were unforeseen events, sick leave and storms, just don't hold up," he said in a statement.
"If they're planning another mass cancellation of train services they have to tell the travelling public about that in advance."