The executive was yesterday accused of conducting "government by paralysis" over the party's refusal to commit to the multi-million pound Edinburgh trams project.
Tavish Scott, the Liberal Democrat spokesman on finance and sustainable growth, also called for an "immediate" statement on the executive's plans, warning that the current situation was harming Scottish transport.
Alex Salmond, the First Minister, told parliament last week that the new executive wanted to review the plans for the £600m trams scheme, along with the Edinburgh Airport Rail Link (Earl) project, amid concerns that they do not offer the best value for money.
Both schemes were approved by the previous parliament, but Mr Salmond warned that the new executive could over-rule that decision if it wanted to.
Yesterday, Mr Scott said it was vital that the SNP set out their plans straight away.
He said: "This is government by paralysis and it cannot be allowed to continue.
"The executive must publish a clear statement of intent immediately.
"Their procrastination and spin over this issue is causing enormous harm to the future of Scottish public transport."
Jack McConnell, the Labour leader and former first minister, last week challenged Mr Salmond on the tram scheme and the airport link, arguing that both were vital to the capital and Scotland as a whole.
However, one Labour back bencher yesterday said he doubted the benefits of the tram scheme to the rest of Scotland and questioned whether it deserved so much support from the public purse.
The MSP told The Herald: "I regard the Edinburgh tram scheme as a local scheme rather than a national scheme.
"What is striking is the amount of public money being spent. It could be argued that most of the benefits of the tram scheme pertain to Edinburgh itself."
John Swinney, the Cabinet Secretary for Finance and Sustainable Growth, last night insisted that his priority was protecting the interests of taxpayers.
He said: "I made clear to parliament on Thursday that this government will not sign off projects that are not robust and financially secure.
"I have called for a financial review of major projects to avoid a repetition of the situation on the Stirling-Alloa- Kincardine rail line, where the cost overrun is now more than 100%. This work is being undertaken as an immediate priority with the objective of protecting taxpayers."
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