The two companies vying to run ferry services on the west coast have been invited to start preparing their final bids.
Current operator CalMac are going head to head with Serco for the contract to operate the Clyde and Hebrides ferry routes from October next year.
The new contract will run for the following eight years and will be worth up to £1billion.
The process has already prompted a clash between trade unions, CalMac and the Scottish Government over conditions for the contract.
The Rail and Maritime Transport (RMT) union staged three days of industrial action earlier in the summer, while two further strikes were called off following talks.
The unions received assurances that there will be a requirement for the future operator to continue the current CalMac pension scheme.
Both bidders were provided with a copy of the initial invitation to tender (ITT) late last week, and in a highly unusual move, the document was made public yesterday.
Both prospective operators will submit a final tender in December 2015, with the contract due to be awarded in May next year.
Scottish Government minister for transport and islands Derek Mackay said that the document was a first stage in a “fair, open and transparent” procurement process.
Concern had been raised by the RMT about the potential “privatisation” of the services if Serco is awarded the contract, which has been refuted by Mr Mackay.
He said: “It is also important to reiterate that no matter the outcome of the procurement process, Scottish Ministers will retain control of all of important issues, such as fares and timetables, through the public service contract.
“Vessels and port infrastructure will also remain publicly owned as they are now.
He added: “As minister for transport and islands, I’m well aware of the vital role these ferry services play in enabling continued and sustainable economic growth for the islands.
“We are focused on ensuring a fair and open competition that leads to getting the very best deal for all of the communities of the Clyde and Hebrides.”
The contract more than 20 routes stretching from the Western Isles to Kintyre which are currently served by CalMac.
Serco was awarded the contract to operate the Northlink routes to Shetland and Orkney in 2012, which had previously been run by CalMac’s parent company.