Unions have lobbied the Scottish Parliament as part of their fight to stop the proposed tendering of Caledonian MacBrayne ferry services.
Unions protested with a large map of Scotland
The CalMac unions, supported by the Scottish Trade Union Congress (STUC), claim any tendering will lead to less efficient services.
The knock-on effect, they said, will bring additional costs to the taxpayer.
But Jack McConnell refused to rule out using private firms during First Minister's Questions Time on Thursday.
Mr McConnell was challenged on the issue at Holyrood but insisted ministers would not break European Union law which requires them to allow companies to bid against CalMac for the west coast routes.
He said government lawyers have said EU state aid rules, enforced by the European Commission, mean the Scottish Executive must open up the tendering process.
Since December, when parliament rejected the plans, Transport Minister Nicol Stephen has been in talks with the commission in a bid to broker a deal.
Answering comments made by Scottish Socialist Party MSP Carolyn Leckie, who accused the leader of "hiding" behind European regulations, Mr McConnell said the discussions with Europe would continue.
He said: "We will stay within the law but we will do all we can to ensure that whatever process is in place, that process protects the high-quality workforce and protects services that are vital for Scotland's passengers, for local people and for tourists."
The first minister insisted it was better for ministers to work with the Commission to secure "the best possible outcome" for island communities and CalMac workers.
He claimed to do otherwise would risk routes being tendered individually, rather than as one contract, with the possibility of the most lucrative services being cherry-picked by private companies.
CalMac is a publicly-funded company which is wholly-owned by the executive.
The unions involved in the campaign to prevent tendering from going ahead are the RMT, Numast, the TSSA and the T&G.
The general secretaries of the RMT and the STUC, Bob Crow and Bill Speirs, were both at Holyrood as part of the union-backed lobby.
Mr Crow said the government must resist the temptation to bring private companies into the equation.
He said: "It threatens the jobs of CalMac workers, half of whom live in the very communities that the ferries serve - and that would undermine the island economies.
"Rather than rushing to embrace this process, the executive should be looking to find ways of protecting CalMac from it, and if necessary mounting a legal challenge to it."
STUC general secretary Bill Speirs added: "The more we examine the proposals, the less they make sense.
"The communities, including my relatives from Stornoway to Staffin, who are reliant on the lifeline services are very apprehensive about what the future may hold.
"Despite the claims of the Scottish Executive in their pursuit of this deeply unpopular action we do not believe tendering is necessary and many support our view."
He also pointed to recent research by the University of Edinburgh which said tendering was unlikely to bring "any discernible benefit" to the ferry routes.
Prior to the Holyrood debate Numast assistant general secretary Mark Dickinson had urged members to write to their MSP about the proposals.
He said: "Along with the other CalMac unions, Numast is concerned about the implications of putting the services out to tender and the potential for adverse effects on members' jobs and conditions and the negative impact on local communities."
Both the SSP and the Scottish National Party have backed the campaign to prevent the tendering process.
On Thursday, the SSP demanded to see the executive's cost estimates and legal advice on the privatisation proposals while the SNP said ministers had shown "no evidence whatsoever" to substantiate their claim that by not tendering they would break European law.