For decades, public pension systems have been doling out more than they take in. Labor unions have stymied reform efforts, but the latest estimates of the public pension gap may finally serve as a wake-up call.

A new study from Moody’s Investors Service, the bond credit rating business, reports that the level of unfunded liabilities for the 25 largest state and local U.S. public pensions is now more than $2 trillion. The gap is more than three times higher than it was just a decade ago.