Ferry operator Caledonian MacBrayne has confirmed it is considering sailing to Lewis on a Sunday.
A Sunday ferry already links Harris and North Uist
The company said it had received "a number" of requests for seven-day sailings to Stornoway and would now hold discussions with the council.
Such a move would be fiercely contested by churches and supporters opposed to Sabbath sailings.
The ferry company said it would consult on the matter, which could go before the Scottish Government.
CalMac said a report on the feasibility of sailing to Lewis on Sundays would go to its board in Fort William at the end of November.
Currently only two of the firm's routes in the area do not operate on a Sunday - the sailing between Tarbert on Harris and Uig on Skye and also the crossing between Stornoway and Ullapool on the Scottish mainland.
A spokesman for the ferry company said: "CalMac will continue to take due notice of the views expressed, which will represent a wide range of opinions.
"The tender specification for the west coast lifeline services noted the sensitivities about Sunday sailings to and from certain communities.
"If considered appropriate, CalMac will refer the matter to the Scottish Government, as it would need to approve any timetable changes brought forward in relation to seven-day sailings."
Councillor Donald Manford, the chairman of transportation at Western Isles Council, said it was opposed to the introduction of Sunday sailings on the Stornoway to Ullapool route.
He said: "Clearly Caledonian MacBrayne has upped the ante on Sunday ferry sailings."
Mr Manford said the council's "policy position remains one of opposition to the introduction of ferry services on the Stornoway-Ullapool route".
However, he said: "We look forward to engaging with CalMac on this issue where we can assess and evaluate the information that they have."
Most shops and licensed premises across Lewis close on a Sunday. There is, however, a scheduled air service to the mainland.
A Sunday ferry service from the south of the island, across the Sound of Harris to the smaller island of North Uist, started last year despite opposition from some local people.