Mike Tyson might have made a tent peg of Michael Spinks in round one, but Merv Lavigne and the Ontario Public Service Employees Union are already into round three. The amounts at stake - a combined purse of $38 million for Tyson vs Spinks, $1.36 for Lavigne vs OPSEU - may be disproportionate, but what's really at stake in both fights isn't money. It's Pride. Dignity. Compulsory union dues.

Lavigne, you'll remember, is the community college teacher from Haileybury, Ont. who objects to his union dues being used to support political causes, and has challenged the practice under the Charter of Rights.

Though he is not a member of the union, Lavigne must pay dues under the ''Rand Formula.'' In the first round of the case, Mr. Justice John White of the Ontario Supreme Court ruled that, while this infringed Lavigne's freedom of assocation, it could be excused under the Charter's ''reasonable limits'' clause to the minimum extent ''demonstrably justified'' by some overriding social objective.

The use of compulsory dues to finance collective bargaining, he ruled, qualified. Higher wages and benefits negotiated by the union benefit everyone under the contract, he reasoned; hence dues must be collected from everyone, to prevent ''free-riding.'' But the use of dues for contentious political causes went beyond this strict test of necessity. The portion of Lavigne's dues used for this purpose - $1.36 - should be refunded.

At first glance, this might seem reasonable enough. Many union members doubtless agree that support for the Sandinistas wasn't part of the deal when they signed on as pit foreman. But, as the unions have argued, neat distinctions between ''political'' and ''bargaining'' uses of union dues don't stand up.

Labor history is sprinkled with cases of strikes and other collective actions that have toppled governments or forced changes in legislation. By the same token, union lobbying on social issues will often affect the scope and outcome of collective bargaining efforts. If indexed pensions are made mandatory, or if daycare is publicly funded, that's two less issues to have to worry about at the negotiating table. If the rules on the use of strikebreakers or secondary pickets are changed, that can tip the balance of power between union and employer.

But put it another way. Suppose a worker honestly objects to the use of his dues for collective bargaining, on principle. Like any cartel, unions seek through collective action to force the price of their labor above what each worker could command in a free market. Those inside the ring get higher wages; others, since the supply of labor exceeds the demand, are locked out of the market. Suppose a conscience-stricken worker wishes to protest this conspiracy against the unemployed, just as Lavigne objects to abortion. What's the difference?

Or, less nobly, suppose he's not thrilled at the idea of having to go out on strike every so often, or worries that he might be one of those let go if inflexible wage demands force layoffs or plant closures. He might well decide, notwithstanding the higher wages collective bargaining might bring, that it's not worth it. He's not free-riding; given the risks, he'd prefer lower wages.

Of course, it may be that he is free-riding, but there's no way of knowing. And as long as the matter is in doubt, the case hasn't been proven that coercive union dues are necessary and those who would restrict the worker's freedom of association haven't shown such limits are ''demonstrably justified.''

If it's okay to force a worker to pay union dues towards the costs of collective bargaining purposes, it should equally be acceptable to turn them to political purposes. But likewise, if one isn't kosher, neither is the other. In other words, the import of this case is that the collection of compulsory union dues, regardless of the uses to which they are put, in itself is a violation of the Charter of Rights.

CARTEL DISCIPLINE

It's possible to question whether Lavigne is really forced to pay dues. If he doesn't like it, unions ask, why doesn't he just take another job? And if this reasoning applies to unions and their members, why shouldn't it also apply to a corporation's use of shareholders' funds? For the same reason we don't treat unions like corporations, and prosecute them for price-fixing.

The law recognizes it's not as easy to pick up and change jobs as it is to buy and sell shares. There's a balance to be struck, here. We rightly allow unions to operate like cartels in negotiating with employers. But that's no reason to put the state at their service, as an enforcer of cartel discipline.

The Charter is taking us into deep waters these days, and deeper still beyond. It may be, ultimately, that we will see the notion of ''economic rights'' - that private contracts, freely entered, that do not impinge on the rights of third parties, should be inviolate - gain firmer legal status. That would outlaw, for starters, minimum wage and rent control laws. But then, judges are political creatures, too, and might prefer not to expose the Charter to the collectivist storm that would blow then.