Transport Scotland is considering a 17-mile tunnel between Rarnish on Benbecula and Neist Point on Skye.
The project is now on a list of potential infrastructure projects that could take shape over the next 20 years.
Supporters believe it would improve quality of life and economic growth of the islands by making travel easier for residents, workers and business by removing “curfew” and cost of ferry services.
The Transport Scotland review comes amid a commitment on the islands to examine ‘fixed links’ to connect the entire length of the Outer Hebrides by road, from Lewis in the north to Vatersay in the south.
Councillor Calum MacMillan (Alba Party), who represents South Uist, Eriskay, Barra and Vatersay Ward, said: “If you have a tunnel, it removes the curfew of ferry traffic.
"People say ‘oh a tunnel will bring all sorts of people here’ but considering we used to have the RAF and 3,000 soldiers based here, it is not as though we are not used to seeing people here.
"It is called the Long Island for a reason. We are the same people, we have the same values and the same principles.
"When you have a tunnel like this, you just don’t have the disconnect of a ferry journey. When you have these fixed links, people just travel back and forward. Think of it as a magic carpet, it takes you right across the islands.”
He pointed to the Eriskay causeway, which links the island to South Uist, and the impact of the Ryfast and Rogfast underwater tunnels that connect Stavanger in Norway to regions in the north and west.
He said: “Eriskay has come back to life over the last 20 years given the number of houses and the number of people who are able to live there and commute to the Uists and Benbecula.
"You look at Stavanger and the tunnels there, you see the infrastructure improvements that the Norwegians have done, and we are far, far behind.”
Those travelling from Benbecula to the mainland currently take a ferry from Lochmaddy on North Uist to Uig on Skye, a journey of 2 hours and 10 minutes, before heading for the Skye Bridge.
An alternative route goes from Lochboisdale on South Uist to Mallaig (3 hours 30 mins) or to Oban (5 hours 10 minutes).
Hector Stewart, of Kallin Shellfish, North Uist, said he “definitely ” supported a tunnel link.
He said: “The ferry service has deteriorated to such an extent that in several years I think it is going to be completely unreliable for a business. The transport issue stops us being able to fulfil orders.”
Current timetables made it difficult for drivers to get to Larkhall in South Lanarkshire in time to make connections for onward transportation to the Continent, he added.
Mr Stewart said he believed a tunnel made “economic sense” given the “drain” that ferry services made on the public purse.
Transport Scotland has been contacted for a comment.