CalMac have announced that passengers travelling between Stornoway and Ullapool must now be on the vessel a minimum of one hour before it sets sail.
This is an increase from 45 minutes, which CalMac say is necessary because of traffic congestion.
The ferry firm says congestion is especially busy at Ullapool, where the sea front has been grid-locked at ferry arrival and departure times.
CalMac says this congestion is caused by late passengers arriving by car at the same time as freight vehicles.
A spokesman for CalMac said: “ It is important that ferry traffic does not adversely affect traffic flow on public roads around the ports.
“We are hopeful this alteration to check-in times will address the issue.”
CalMac also confirmed that the MV Loch Seaforth will be in dry-dock for maintenance from October 26. It will be replaced temporarily by its Clyde-built predecessor the MV Isles of Lewis.