Hundreds of people have backed a campaign against plans to replace the Saltire outside Angus council offices.
An artist's impression of the new Angus flag design
The local authority has approved proposals to create a new flag based on the council's coat of arms, at a cost of more than £4,000.
The standard would be raised outside 10 key buildings across the region instead of the national flag.
Critics have set up an online petition against the idea, which has so far attracted more than 1,000 signatures.
The measure was agreed by the Angus Alliance, a coalition which replaced the SNP as the ruling administration at the last election.
SNP councillor Donald Morrison told the BBC Scotland website that he thought the decision was "wrong".
The representative for Arbroath East and Lunan said: "Speaking as a Scot, I feel quite hurt that they're taking the Saltire down and replacing it with the council flag.
"I think it is a political decision from a tiny minority of the administration which was seeking revenge for all the years of opposition.
"They've not listened to the members of the public who have signed this petition, so many people from all political persuasions, angry at them for taking down our national flag."
A number of petition signatories have strongly criticised the move on the website.
Iain Higgins called it a "shocking waste of time and money", while Duncan Fenton demanded "keep the Saltire - replace the council".
Greig Holmes pointed out that Angus was where the Declaration of Independence was signed in 1320.
He added: "Bruce and Wallace will be turning in their graves."
Fellow commentator Alex McDonald accused the council of treachery.
He said: "This is an absolute disgrace, and a betrayal of our national flag."
Councillors in Angus recently approved the plan, which was put forward by the local authority's chief executive, David Sawers.
In a committee report, Mr Sawers said: "The matter of flag flying is one for individual local authorities to determine.
"At present the Saltire is flown on key council buildings within each of the burghs and is only replaced by the Union flag on Remembrance Day or for certain Royal events.
"It has been suggested that it would be more appropriate for a flag that represents Angus uniquely to be flown at key council buildings and for this flag to be based on the council's Coat of Arms."
There has been talk of a compromise, where additional flagpoles would be erected so both the Saltire and the Angus flag could fly over council buildings.
The design consists of four quarters containing a crowned lion passant, a cinquefoil, a checked strip crossed with buckled belt and a depiction of the heart of Robert the Bruce to represent the four ancient earldoms of Angus.
Ten flags would be ordered from a specialist maker, at a cost of £450 each.