Western Ferries has unveiled a £4m investment in improving berthing and terminal facilities on its Gourock to Dunoon route.
The Sound of Sanda ferry sails from McInroy's Point at Gourock
The company said this would involve new linkspans, increased car parking and improved passenger facilities.
It said the plans would proceed regardless of the outcome of tendering for the parallel Cal Mac route, which the firm has been bidding for.
Opposition parties have raised doubts about the tendering process.
They said the Western Ferries move was an indication that confidence in the process was collapsing.
However, a Scottish Executive spokesman gave an assurance that all bids were being assessed with scrupulous fairness.
Western Ferries has declined to comment on the claims.
It has run a commercial operation between Gourock and Dunoon for 30 years, competing against Cal Mac's subsidised service.
The two companies, and rival bidder V Ships, were invited to tender for that service in July.
Scottish National Party spokesman Jim Mather said he has raised concerns over the competence and integrity of the tendering process
Conservative spokesman David Davidson said several potential bidders had complained to him about its handling.