AFTER the Supreme Court rejected her bid to overturn the law governing taxation of child-support payments, Suzanne Thibaudeau charged that she was the victim of sex discrimination twice over: once by the law itself, and once by the Supreme Court's upholding of it. "Laws are made by men for men," she announced.

So it is that one of those men, Justice Minister Allan Rock, is under enormous pressure to change the law, notwithstanding the court's ruling. Many divorced women feel that the obligation to pay tax on the child- support payments they receive from their ex-husbands is discriminatory: Though the tax nominally applies only to the "custodial parent," in almost every case that is a woman.

To compound the seeming unfairness, the non-custodial parent - the man - is allowed to deduct the same payment from his income for tax purposes. One pays the tax, one doesn't. One's a woman, the other's a man. Discrimination, right?

It would be, if the two were in similar circumstances. But they aren't. One has the children, the other doesn't, of course. More to the point, he pays the support, she receives it.

Child support is not a discretionary expenditure: The man is legally required to pay it. In some provinces, it is deducted from his pay cheque, just like a tax. It is not available to him as income. It is, however, available to her. It makes no difference that it is called "child support." It's all part of her total income, some part of which is spent on the children, some on other things. Someone has to pay the tax. Logically it should be her.

Or should it? There's often a difference between who the tax law says pays the tax, and who actually pays it. Although it's officially the parent in receipt of the child-support payment who pays the tax, judges in divorce cases are supposed to "gross up" the amount of support they award to reflect the tax liability. Which means the man is the one who effectively pays the tax, even though the law says the woman does. But then he gets to deduct the full amount from his taxable income, which means Revenue Canada picks up part of the tab.

Since the man usually has a higher income than the woman, and hence is in a higher tax bracket, the total tax owed between them is less than if he paid the tax instead of her: about $330-million less. The divorced couple in this case would in fact pay less tax than if they were still together, where such "income-splitting" would be disallowed. For some, this is discrimination of another kind: against married couples. But others, including the Supreme Court, cite this implicit subsidy as a benefit: With less tax to pay, that should leave more for child support.

That's the way the system is supposed to work. Much of the time, however, it doesn't. Judges don't always gross up the award properly to take account of the tax. Many ex-husbands, as is well known, don't pay up. There may not be a tax saving, if the woman is in a higher tax bracket; and if there is, the man may not pass it through in higher payments.

For the most part, however, these are complaints about the entire system of child support - not the particular question of who, at least in legal terms, pays the tax. In which case, the remedy would seem to lie in standardized guidelines for calculating child support and tougher enforcement of support orders. Simply reversing the charges would raise inequities of its own.

Or would it? If the non-custodial parent is supposed to bear the burden of the tax anyway, why not acknowledge that in law? One reason is that, without the deduction, he would be bearing the full amount of the tax burden. So those men currently paying child support, at levels that were set with the deduction in mind, would be back in court applying to have their payments lowered. On a net basis, divorced women with children might end up worse off than before - even though they would no longer be paying tax on their payments.

The (now-defunct) Canadian Advisory Council on the Status of Women had an answer to that. Convert the tax deduction to a 17-per-cent tax credit, up to a ceiling of, say, $5,000 per child. Men in the lowest tax bracket would see no change in their position; only men higher up the income scale would pay more tax. The revenue gained could be used to offset the cost of exempting women from the tax. Another option, raised by a federal- provincial task force on child support, would give divorced couples the option of who should pay the tax, assuming they could agree on this - assuming they could agree on anything.

But the two ex-spouses are not the only people whose interests have to be considered. Exempting child-support recipients from tax, for example, would be unfair to single mothers without this source of income. Take two single mothers: one divorced, one never-married. Each has a total income of, say, $30,000. But where one earns the whole $30,000 in wages, the other earns $25,000, and gets $5,000 in support. Same total income, same costs of living, yet one would pay less tax. Just as the taxation issue is in some ways a proxy for problems with the child-support system, so the problems of child support are part of the perennial issue of paying for the kids. Parents of any description already receive a federal tax credit that is supposed to account for the costs of child care: the child tax benefit. If that's not enough, then it would seem only sensible to increase it for everyone - or everyone who needs it. But why single out divorced parents for special treatment?