It may have been the least surprising U.S. Supreme Court decision in history.

Ruling on a case from Illinois, the court, by a 5-4 vote, declared last week that compelling non-members of public employee unions to pay dues violates their free speech rights.

For years, the conservative majority had indicated that it wanted to overturn a previous decision that allowed unions to collect so-called “agency fees” from non-members in states, such as California, that sanctioned the practice.

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The theory of agency fees was that since non-members benefit from contract negotiations, they should be compelled to contribute to their unions’ non-political activities.

The court held, in effect, that it was impossible to separate political and non-political activities, so non-members were being compelled to finance political positions that they might not support.

“The First Amendment is violated when money is taken from non-consenting employees for a public-sector union; employees must choose to support the union before anything is taken from them,” the opinion, authored by Justice Samuel Alito, declared.

The court was ready to act in a previous case out of California, but Justice Antonin Scalia’s death in 2016 left it tied 4-4 on the issue. Very soon afterward, however, the Illinois case reached the court and President Donald Trump’s nomination of Neil Gorsuch as Scalia’s successor restored the conservative majority.

So unions knew it was coming and had been doing what they could to cushion its potential blow to their finances.

Losing agency fees from the relatively few non-members who pay them now would not have a major effect. The greater fear among public employee union leaders is that making dues voluntary would entice substantial numbers of current members to drop out.

Estimates of membership losses have ranged up to a third, but different unions probably will see different effects.

It seems likely that unions representing relatively highly paid professionals, such as teachers, engineers, police officers and firefighters, will not see huge membership declines. However, unions of lower-paid clerical and support workers, to whom union dues represent substantial financial burdens, could see serious membership erosion. And if it occurs, those unions ability to distribute campaign funds and otherwise influence politics could also decline.

The cases that resulted in last week’s decision were pushed by anti-union organizations and in theory, a loss of union political clout would be a gain for countervailing interests, such as business and taxpayer groups.

California’s unions have long been preparing for the decision, persuading union-friendly Democrats in the Legislature to enact a series of protective laws, such as requiring new workers to attend union “orientation” meetings and allowing unions exclusive access to workers’ contact information while barring others from having it.

This year’s crop of budget “trailer bills” contains even more reactive provisions, such as making those orientations secret and making it more difficult for workers to stop paying dues.

However, the latter provisions could run afoul of the Supreme Court’s declaration that “neither an agency fee nor any other form of payment to a public-sector union may be deducted from an employee, nor may any other attempt be made to collect such a payment, unless the employee affirmatively consents to pay.”

It could require unions and/or their employers to almost immediately ask current members whether they want to continue having dues deducted from their paychecks.

Those inquiries could be, in effect, entirely new representation elections. And that’s when the real impact of the decision would become evident.