Portadown braced itself for a repeat of the 1996 stand-off yesterday as Orangemen vowed to attempt to follow their traditional route along the Garvaghy Road despite the Parades Commission's ruling.
Business people said they expected a complete shutdown at the weekend.
There was an obvious increase in tension in the town as news spread that the parade was to be rerouted.
A checkpoint, manned by police in fireproof boiler-suits, was set up on the main street. The leader of the breakaway Spirit of Drumcree group of Orangemen, Mr Joel Patton, said they would protest at the decision.
"The Grand Lodge is the body responsible and is drawing up tactics for this, but I suspect what they will do is employ a campaign of people's resistance to this, but it will be peaceful resistance, and they will be saying that you cannot subjugate the people's culture," he said.
Mr David Jones of Portadown District Lodge said he felt disgust at the decision and also "a degree of foreboding".
He regarded the Parades Commission as "a law-breaker's charter". Local Orange Order officials were due to meet in Portadown last night to draw up plans for next Sunday.
Mr Jones said: "On the day itself our intention would still be to parade to our church service, hold our church service, and to return via our traditional route, or as far as we can along that traditional route." It is expected that Orangemen from other areas will gather at Drumcree on Sunday to protest at the decision.
Under the legislation, the RUC Chief Constable can ask the Northern Secretary to overturn the Parades Commission's ruling on the day of the parade for security reasons.
Mr Jones said Orange lodges in other areas would decide themselves what action to take.
"We can't prevent anybody from coming. We don't have the authority to do that. The only thing I would be cautioning people to do is to have cool heads and calm nerves, that some people don't have a knee-jerk reaction."
The Orange Order's County Grand Master in Co Armagh, Mr Denis Watson, said a legal challenge would be made against the decision, because the Order had filed an application to parade before the new legislation came into effect on April 2nd.
"Whether the Parades Commission can legislate for this parade is open to question," he said. This legal challenge is unlikely to be successful.
Mr Watson, who was elected to the Northern Ireland Assembly in Mr David Trimble's Upper Bann constituency last Thursday, said the Parades Commission was "an anti-Orange quango". It was too early to say what action the Portadown District would decide to take, but any protest would have to be peaceful.
"We would be appealing that people do not take any action that would bring discredit on the colour they wear as Orangemen." Mr Watson said he believed "thugs were there waiting to come in on both sides".
The Grand Orange Lodge of Ireland issued a statement yesterday, condemning the decision. "This infringement of civil liberties by a quango is totally reprehensible," it said, adding that the Grand Lodge would consult with officers of Portadown and Co Armagh before deciding on a course of action.