Mr Macsween has openly campaigned for Sunday sailing
A senior councillor has quit his post following the row over introducing Sunday ferries to Stornoway.
Donald John Macsween, vice-chairman of transportation, said he could not support Comhairle nan Eilean Siar's policy of opposing seven-day sailings.
Mr Macsween, a member for Point ward, has openly campaigned for Sunday sailings over the last nine years.
He was due to be part of a council delegation meeting ferry operator Caledonian MacBrayne on Friday.
Mr Macsween, who is standing for Labour against MP Angus MacNeil at the next election, has succeeded in two hotly-contested local elections since he went public with his support for Sunday sailings, despite warnings from church figures that he would not survive in island politics.
In a letter to the chief executive of Comhairle nan Eilean Siar (Western Isles Council), he said he had always been a strong advocate of seven-day transportation links with the mainland.
"I now find myself in the position where I cannot, in all conscience, go to the meeting with CalMac on Friday and support the present council policy on seven-day mainland ferry links with Lewis and Harris," he said.
"I will therefore offer my resignation to the next meeting of the transportation committee."
He added: "I still feel strongly on this issue for social reasons but I also realise there is a vociferous opposing view from some. I did not want to compromise myself by arguing from a position which opposed that of the council."
Caledonian MacBrayne is to consult on the idea of Sunday sailings
Meanwhile, the Lewis branch of the Lord's Day Observance Society earlier gave Mr MacNeil and MSP Alasdair Allan 24 hours to "come off the fence" and declare whether they were for or against the development of seven-day sailings.
Campaign manager Angus MacKay said: "We're facing a threat to our way of life here on Lewis that many have yet to appreciate.
"If a Sunday ferry service starts, it'll never be stopped. It'll change the island quickly, it will change it irreversibly and the worst consequences will fall on shopworkers, folk in the service sector and the less well off."
Mr MacNeil said: "If there is one issue that is not best served by megaphone diplomacy or soundbite politics it is surely this one.
"Nobody has asked, as yet, to meet me on this issue.
"If they do, I would be happy to meet with the Lord's Day Observance Society or any other group who feels that it might be useful to talk about the CalMac consultation."
Mr Allan insisted that it was an operational matter for CalMac.
"Personally, I would have preferred that any discussion of this kind had arisen from within the community, rather than been imposed from outside under a piece of UK legislation," he said.
"However, both sides will now have an opportunity to make their views known to CalMac, and I would urge them to make use of the consultation process to the full. I would also urge CalMac to make the consultation a genuinely listening exercise."