The San Francisco board of supervisors (the city council, essentially) today will consider a phone book opt-in ordinance that directory publishers believe will be devastating to their business. The measure, supported by announced mayoral candidate David Chiu, has drawn urgent opposition from the directory publishing industry, as well as local businesses that rely on Yellow Pages leads. Unions representing workers whose jobs would be at stake under an opt-in regime have also joined the fight.

It’s unclear whether the measure will face a vote today, but so far it has sailed through all the steps leading up to a final vote, so passage seems possible, if not likely.

The San Francisco measure is the toughest yet proposed in a major U.S. city. Seattle recently passed a tough opt-in bill, which prompted an industry lawsuit. Seattle has since modified the bill, but the lawsuit remains active.