Independent consultants have been called in to look at the effect of tolls on the Forth and Tay bridges.
There is local opposition to tolls remaining on the Tay Road Bridge
They will look into the economic, social and environmental impact of scrapping or retaining the tolls.
Transport Minister Tavish Scott, who had previously promised a review of tolling on the bridges, wants a report by the end of the year.
The move was criticised by opposition parties, with the Tories describing it as a "delaying tactic".
Ministers have been under pressure to abolish the Tay and Forth charges. Tolls on the Erskine and Skye crossings have already been scrapped.
The Scottish Executive is now asking for the opinions of relevant people and organisations on tolling, which will be analysed before an initial report is drawn up.
A team of consultants will be appointed by the end of the summer.
Mr Scott said: "This additional work will consider the economic, social and environmental impact of tolls. MSPs and others will want to submit factual evidence to this study.
"I look forward to looking at that evidence."
However, Tory deputy leader Murdo Fraser condemned the study as "yet another delaying tactic".
The Mid Scotland and Fife MSP said: "We have already seen a huge amount of time, effort and expense taken up on the inquiry into bridge tolls across Scotland."
Ministers have been under pressure to scrap tolls on the Forth bridge
Mr Fraser insisted there was no justification to keep tolls on the Forth Road and Tay Bridges, adding: "The 'detailed study' will add nothing whatsoever to the discussion, except a hefty bill."
Scottish National Party Mid Scotland and Fife MSP Bruce Crawford dubbed the review "a cynical exercise in punting the matter into the long grass until after the Scottish Parliament elections in 2007".
He has submitted a member's bill to the Scottish Parliament seeking the abolition of tolls.
Mr Crawford said: "The SNP want tolls abolished now, not some vague time in the future, which is why I intend to press ahead with my bill to get rid of bridge tolls."
Scottish Greens transport spokesman Mark Ballard MSP said: "We're very sceptical about the reasoning behind this new review because the executive has just completed a comprehensive two-phase review of Scotland's tolled bridges.
"The previous reviews found that there would be significant congestion effects from removing tolls - we wonder whether this review will magically come up with a different outcome."