Parents paying child support must declare increases in income to their former spouses and adjust their payments accordingly or face the possibility of making retroactive lump-sum payments, the Supreme Court of Canada has ruled.

"I think it's going to change the way child support is handled in Canada," Deidre Smith, the lawyer for the four Alberta fathers represented in the case, said yesterday.

"Up until now, most families negotiated child support not too long after separation and most families lived with those arrangements despite any changes in their circumstances. What the Supreme Court of Canada has said today is that all support payors have a responsibility to make disclosure of their income whenever there are any changes to their income, and to change their child support when their income changes."

While the payors — in most cases, fathers — are required to report changes in income, it remains up to the payees — in most cases, moms — to enforce payment of the increase through the courts if necessary.

For the first time, the Supreme Court recognized the needs of the father's new family. When it comes to retroactive payments, it ruled: "It is difficult to justify a retroactive award ... where it would cause hardship for the payor parent's other children."

The court was ruling in the cases of four Alberta fathers. Two were ordered to make retroactive payments, and two were absolved from making the retroactive payments.

In one case, the retroactive payment was calculated to be nearly as much as the father's annual salary of $23,000.

The mother's annual household income was $50,000. Her claim was dismissed on the grounds of her former spouse's hardship. A second retroactive claim was dismissed because the resources of both parents were judged to be equal and the mother had not exercised her rights in a timely fashion.

Another father, who refused to provide financial assistance at various times when requested, responding with "acrimony and intimidation," was ordered to pay $100,000 in retroactive payments. A fourth father, who refused to contribute to his daughter's college expenses despite substantial income, was ordered to pay $30,000 in retroactive child support.

Smith said this is the third Supreme Court of Canada decision on child support payments in as many years and the court has been consistent in saying that "one size does not fit all" — the courts need to be flexible to meet the needs of children.

According to the ruling the child support orders should provide payor parents with "the benefit of predictability." Danny Guspie, executive director of Fathers' Resources International, said the ruling is disappointing because it does not appear to make any reference to decreasing child support payments when income declines.

"It's a very cumbersome system. You have to pay $3,500 for a lawyer if you lose your job to get started on a variation. If you've lost your job, how do you do that?"

He said it is a hopeful sign that not all the retroactive payments were upheld.

Grant Gold, a Toronto lawyer and member of the national family law executive of the Canadian Bar Association, said he thinks the decision allows the courts to tailor decisions to suit individual family needs.

"I think you're going to find courts using their discretion and not nailing everybody," he said.

"There's no way it's cut-and-dried. What's more cut-and-dried is, we ought to be telling the payor client, when they're making more money, the safest course is to let the former spouse know." Ross Finnie, a professor at the School of Policy Studies at Queen's University in Kingston and the principal architect of the support payment guidelines, said the ruling is in line with the original intentions of the guidelines.

"The underlying principle established was basically that the non-custodial parent would contribute to the child in the same amount as they would if they were still living together."

He said the rate was pegged at 16 per cent of parental income for one child.