The fishermen at Cove told last year how the landowner wanted the boats removed as he looked to improve the area where they were moored.
However, they have continued to operate.
A legal letter has now been received, giving them a deadline to remove the boats or face court proceedings.
Boat owner Jim Adam told BBC Scotland: "Many people use the facility.
"I find it incredible we have not heard in a year-and-a-half and then we get a letter, which is ridiculous.
"There's no intention to remove anything - we need to stand up for our rights."
Landowner Pralhad Kolhe declined to comment.
A letter from law firm Stronachs on his behalf, dated 26 August, gave a 14-day deadline before court proceedings would commence.
It stated the boat owners had "no right" to store their boats or equipment on Mr Kolhe's property.
The future of a small Aberdeen harbour is once again under threat, with fishermen facing court action unless they remove their boats.