Labour has called for every document relating to the maintenance of the Forth Road Bridge to be made public after it was revealed that some heavy loads were banned from crossing it back in February.
A confidential email released by the party shows that chief engineer Barry Colford ordered restrictions on the passage of vehicles weighing more than 150 tonnes after analysis of the loading on the bridge's truss end links - one of which has since cracked, forcing its closure.
"The restriction needs to be in place until all the truss end links are either strengthened or replaced," he said in the document sent to Lesley Hinds, convenor of Edinburgh City Council's transport, infrastructure and environment committee.
Scottish Labour deputy leader Alex Rowley said the email undermined claims by SNP ministers that the crack was "unforeseen and unforeseeable."
He said: "The fact that as far back as February there were concerns about the safety of the bridge is very concerning.
"We now know the chief engineer was so concerned about the safety of the bridge that certain vehicles were prevented from travelling on it.
"We need full transparency from the SNP Government about this. The idea that problems with the bridge were unforeseen, as Nicola Sturgeon and Derek Mackay have claimed, just doesn't stand up to any scrutiny."
Opposition parties have called for a full parliamentary inquiry into the closure of the vital crossing, which is due to re-open in the New Year.
Mr Rowley added: "We know the SNP Transport Minister misled Parliament when he claimed there was no link between cancelled repair works in 2010 and the damaged area now.
"And we know the SNP Government's budget cuts resulted in vital repair works being put off.
"The thousands of people and businesses affected by the closure of the Forth Road Bridge deserve full transparency."
A Transport Scotland spokesman said: "There is nothing to suggest that the restriction on exceptionally large abnormal loads has anything to do with the current situation.
"Restrictions on loads of this type have little impact as there are very few movements of this size and they are agreed in conjunction with Transport Scotland, local authorities and Police Scotland who escort such loads.
"The defect which has resulted in the closure of the Forth Road Bridge was identified in the last few weeks. It was unexpected and not predicted by previous analysis that was carried out by Forth Estuary Transport Authority.
"The work that was being considered in 2010 was prompted by concern about another part of the truss end link, not the part that is now cracked."