Transport Scotland made the move amid fears a recommendation for a train link would reignite the Glasgow Airport Rail Link controversy.
Consultancy Aecom was commissioned last year by the airport, in partnership with the Government agency and Glasgow and Renfrewshire councils, to carry out an independent study into the best public transport solutions to link the airport to the city.
It is understood that when the company submitted its shortlist in April, officials at Transport Scotland became nervous the inclusion of heavy rail among the dozen recommendations would call into question their decision to axe the £210 million Glasgow Airport Rail Link development four years ago. At the time scrapping the rail project outraged the Labour-led Glasgow and Renfrewshire councils.
The shortlist's publication has now been delayed for five months, exasperating groups involved and stalling Aecom's team from drawing up costings for each option.
James Kelly, Scottish Labour's spokesman on infrastructure, said: "It's disgraceful that Transport Scotland has delayed the publication of this report simply because the conclusions do not say what it wants. Keith Brown must ensure this study is published, in full, immediately.
"It is common sense that a rail link would be a suitable transport solution to accommodate the projected passenger growth for Glasgow Airport, that's why the project should have gone ahead and why business leaders strongly opposed its cancellation."
Digging was already under way at Glasgow Central Station when the Scottish Government pulled the plug on the project in September 2009. The link, which would have seen trains running to and from the airport and the station every 15 minutes, was supposed to be partially finished in time for the 2014 Commonwealth Games.
Councillor Alistair Watson, Glasgow City Council's spokesman for transport, said: "We are calling for the full publication of the consultants' report because the council has always believed heavy rail working in conjunction with Crossrail is as strategically important to Scotland's economy as the M74.
"There was a lot of anger across the city about the decision to scrap the Glasgow Airport Rail Link, but also a great deal of dismay and, frankly, suspicion about how it was handled."
Renfrewshire Council leader Mark Macmillan said: "We believe a rail link in some form continues to be a viable and practical option. It's essential all those involved have available transparent and independent assessment to inform that debate."
An airport spokesman said: "We have always supported the need for a fast, direct and reliable link between the airport and the city centre ... this important study will identify the means by which we can move forward and improve access to the airport."
Transport Scotland denied witholding the findings and said the report was "still being finalised".