The Scottish Defence League (SDL) unveiled plans to hold a "respect vigil" at the town's memorial to the 270 people who died when Pan Am flight 103 was blown up over Dumfriesshire.
The group, which says it is against the "Islamification" of Britain, also wants to use the event as a protest against Justice Secretary Kenny MacAskill, who was branded a "traitor" over his decision to release Libyan bomber Abdelbaset al-Megrahi.
On Monday, Scotland United released a statement saying the SDL and its sister organisation, the English Defence League, should not be allowed to demonstrate in Lockerbie. The group is backed by all of Scotland's mainstream political parties, as well as trade unionists, charities and faith groups.
In a statement, undersigned by supporters, Scotland United said: "We strongly oppose plans by the Scottish Defence League and English Defence League to demonstrate in Lockerbie. The SDL is a racist group whose aim is to divide us by making scapegoats of one community, just as the Nazis did with the Jews in the 1930s.
"Whatever one's personal or political views on the release of Mr Megrahi, we believe that such a march is totally inappropriate and a cheap publicity stunt. Any attempt to use Lockerbie would cause further distress and suffering to those who have lost loved ones and would be abhorrent.
"We have a simple message for these racist and fascist groups. There is no place for your organisation in Lockerbie or in Scotland, and we condemn any organisation that wishes to capitalise on the murder of 270 innocent men and women. We call on the SDL and all other groups to cancel their action and stay out of Lockerbie."
Dumfries MSP Elaine Murray has also lodged a motion in the Scottish Parliament, blasting the SDL and EDL's plans as "deplorable" and calling for the march to be called off.
The Scottish Defence League denies it is a racist or violent organisation. In the limited public content on the group's Facebook site, it states: "This group is for people that can join us to protest the Muslim extremists that support terror in our land and burn our national flag."
The group has worked to keep details of planned actions more secret, since police prevented some members entering Edinburgh for a planned march last month.
