OTTAWA -- Federal lawyers say Ottawa has no special obligation to those who've fought wars on behalf of Canada and that it's unfair to bind the Harper government to promises made nearly a century ago by another prime minister.

The assertion is spelled out in black and white in a statement of defence filed by the Justice Department in a class-action lawsuit by Afghan veterans who claim a 2006 overhaul of benefits is discriminatory under the charter of rights.

The court papers, filed in January, were made public Tuesday, the same day Prime Minister Stephen Harper greeted the last wave of soldiers returning from the now-concluded mission in Afghanistan.

The Conservatives, who've built political capital on supporting the troops, are planning a day of commemoration for the mission, which lasted a dozen years, on May 9.

At the same time, federal lawyers argue that the lawsuit, if successful, would put disabled veterans ahead of all other Canadians in terms of their compensation and treatment by the federal government.

The B.C. court filing, obtained by The Canadian Press, also states that there is "social contract" between the nation and its soldiers whom are called upon to lay down their lives without question.

At issue is a 1917 pledge made by Sir Robert Borden, the country's prime minister during the First World War on the eve of the Battle of Vimy Ridge, which said:

"You can go into this action feeling assured of this, and as the head of the government I give you this assurance: That you need not fear that the government and the country will fail to show just appreciation of your service to the country and Empire in what you are about to do and what you have already done.

"The government and the country will consider it their first duty to see that a proper appreciation of your effort and of your courage is brought to the notice of people at home that no man, whether he goes back or whether he remains in Flanders, will have just cause to reproach the government for having broken faith with the men who won and the men who died."

The statement was nothing more than a speech by a politician; it cannot be considered applicable today, and was never legislated, federal lawyers stated.

"The defendant pleads that the statements made by Sir Robert Borden and the coalition government in 1917 were political speeches that reflected the policy positions of the government at the time and were never intended to create a contract or covenant," said the 37-page court filing.

"It is further pleaded that at no time were these statements intended to bind future governments and, in any event, the principle of parliamentary sovereignty would have prevented such a result had it been intended."

The defence goes on to say Borden's statement was simply a policy position and Parliament, within the limits of the constitution, "has the unfettered discretion to change or reverse any policy set by a previous government."

The position taken by federal lawyers is bound to further sour already bitter relations with the veterans community, which is still smarting from the closure of eight regional veterans affairs offices in January.

The lawsuit was originally filed in B.C. Supreme Court in October 2012 and involves six veterans of the Afghan war.

The soldiers are suing over the new veterans charter, which provides workers-compensation-style lump sum payments to wounded vets for non-economic losses, such as losing limbs, as opposed to the pension-for-life settlements provided after previous wars.

The allegations in the lawsuit have not been proven in court.

The notion that Ottawa has no special obligation to its soldiers first appeared last summer in court papers when federal lawyers tried to get the class-action dismissed.

Last fall, a Federal Court judge shot down the attempt to halt the case -- something the Harper government is now appealing.

The Royal Canadian Legion described the government's position as "reprehensible" last October.