WASHINGTON taxpayers got good news this week as the state Supreme Court ruled against a pair of pension lawsuits filed by public employee unions that would have cost the state billions. But a new state analysis shows an even bigger budget-buster is on the fall ballot, in the form of a class-size initiative from the Washington Education Association — Initiative 1351.

What the pension rulings have in common with I-1351 is that they have been the biggest questions hanging over the Legislature before next year’s serious school-funding wrangling begins. The Supreme Court has ordered lawmakers to increase basic-education spending by roughly $3 billion or more — exact cost is a matter of debate. Lawmakers might be able to squeak through without dramatic tax increases or drastic cuts to social services, higher education and other vital programs, as the economy continues to recover. But not if billions of dollars in additional spending is required.

An analysis from the Office of Financial Management illustrates the danger I-1351 poses — at least a $3.8 billion expense every two years when fully implemented in 2019-2021. The measure reduces class sizes in all grades, a noble-sounding goal — except little benefit has been proven after grade 3. Besides, the court’s order already will force smaller classes in lower grades.

The OFM points to an initiative-spurred school-district hiring spree — an additional 7,500 teachers and 18,000 staff. The OFM doesn’t address school-construction costs or teacher pay raises, which the court has hinted it would like to see. Yet, the initiative cynically provides no way to pay the bill, at the worst possible time.

Thursday’s pension rulings offer some relief. Lawmakers goosed benefits when the economy roared in the ’90s, but reserved the right to stop increasing their obligation at any time. They did so a little over a decade later, when the cost became apparent. Unions and retirees argued no benefit might ever be revoked, but the court rightly said legislation was clear.

The court eliminated a threat to state and local governments estimated at $1.3 billion in the next budget, $10 billion over 25 years. Washington voters need to be just as sensible in November when they consider the effect of I-1351.

Editorial board members are editorial page editor Kate Riley, Frank A. Blethen, Ryan Blethen, Sharon Pian Chan, Jonathan Martin, Erik Smith, Thanh Tan, William K. Blethen (emeritus) and Robert C. Blethen (emeritus).