The opportunities an Argyll to Ayrshire ferry service could offer are being highlighted by Argyll and Bute Council and South Ayrshire Council in a letter to Keith Brown.
It comes ahead of the Scottish Government Ferries Plan, which is due to be published soon.
The draft plan, first published a year ago, mooted linking Kintyre to Ayrshire by Arran.
But the two councils say they are committed to supporting the development of a Campbeltown to Troon route. The authorities are also looking to explore interest in a triangular route with the Northern Ireland Executive.
Deputy Leader of Argyll and Bute Council, John Semple said, "I believe an Argyll-Ayrshire service would bring significant benefits in both directions.
"We both have much in common and also much which would complement the existing strengths and opportunities which our communities have.
"The service could also relieve freight pressures on the A83 and reduce transport emissions."