The Labour Party has launched a fresh assault over the SNP's move to scrap two controversial transport projects.
It will cost over £1bn to bring trams and an airport link to Edinburgh
Labour's Des McNulty said the Scottish Executive's plans to ditch the Edinburgh trams and airport rail link were "blatantly party political".
Speaking in a Holyrood debate, Mr McNulty criticised the decision to carry out a review of the projects.
Transport Minister Stewart Stevenson said it was "natural" to examine whether they offered value for money.
The SNP election manifesto committed the party to redirecting the £1.1bn that the tram and rail link schemes would cost to other areas.
Earlier this week, Finance Secretary John Swinney asked Audit Scotland to look at the methods used for forecasting the costs of the project, and to report back to him by 20 June.
Mr McNulty said the executive had merely set up the review in an attempt to find an excuse to ditch both projects.
He told MSPs that if ministers had "genuinely" wanted further assurances about cost and value for money, they could have asked experts at Transport Scotland to study the figures.
Mr McNulty added: "The selection of these two projects is bluntly, blatantly, party political.
"Ministers presumably hope that Audit Scotland can provide some evidence or finding which would help justify the decisions the SNP desperately want to make.
"But the cloak of Audit Scotland involvement cannot mask the fact that the SNP for now is defying not just the previous decisions of parliament but also the majority view of members of the current parliament."
Mr McNulty warned that each week that went by without a decision being ratified by parliament would rack up the cost of the trams in particular, and cause the project to lose momentum.
He said the collapse of the tram scheme would have a "devastating impact" on the construction industry's confidence in public projects in Scotland.
But Mr Stevenson insisted it was normal to review projects to establish whether they would provide value for money.
Mr Stevenson is concerned over the projects' value for money
"Who wouldn't want to make sure they were still getting the benefits they expected at the price they had been promised?" he said.
"It is completely natural for the new Scottish government to want to look at what we've inherited and check whether it is fit for purpose.
"It is even more normal, natural and necessary to review projects that you have inherited not from the parliament but from the previous administration."
Mr Stevenson said the cost of the Stirling-Alloa-Kincardine railway, due to open this summer, had been estimated at £65m to £70m, only for SNP ministers to be told "within days of taking office" that this had now gone up to £83m.
He added: "It is precisely to bring the necessary objectivity to these projects that we invited Audit Scotland to look at the projects
"We will consider the report swiftly and return to parliament before the summer recess to set out our position clearly and concisely."
Tory transport spokesman Alex Johnstone told MSPs his party backed "sustainable" public transport but there could be no blank cheques.
He said: "It is important that parliament takes decisions on these matters, but it is also important that these decisions are properly informed.
"Therefore the Conservatives welcome the fact that Audit Scotland has been asked to look into these cases and report back this session."
Former Transport Minister Tavish Scott, of the Lib Dems, said if the Nationalists were reviewing the cost of the trams and the airport rail link they should also look at the costs of all other transport schemes.
He said: "Mr Stevenson should be reviewing all the transport projects, not just two of them, if his position on transport was in any way credible.
"This is a political decision and they're trying to find the evidence for it."
The executive won a vote on the issue by 66 votes to 59 with the support of the Tories.