Labour transport spokesman Des McNulty said there had been no proper assessment of what impact the expected increase in traffic levels would have on the lifespan of the bridge or the environment.
He claimed previous studies had suggested the removal of tolls would mean a 15 per cent increase in traffic northbound and 20 per cent southbound.
But after quizzing Scottish Government officials at a meeting of the Scottish Parliament's transport committee, he said: "It's as if they're saying 'There is all this evidence about the impact of abolishing the tolls, but we're going to turn a blind eye to it'."
Mr McNulty told the committee there should have been a strategic environmental assessment of the toll abolition, and he asked what the impact would be on the structural integrity of the bridge of increased traffic and what difference it would make to the date when HGVs may have to be banned.
Chris Rogers, a senior transport official in the Scottish Government, said there was no requirement for an environmental appraisal because scrapping the tolls was simply a financial change, and told the committee the structural integrity of the bridge was linked to the corroded cables rather than the volume of traffic.
Alastair Andrew, general manager and bridgemaster on the bridge, said it had to be accepted congestion was likely to increase.