The city has appealed the firefighters' arbitration award, which the administration says would cost more than $200 million in wage and benefit increases over the next five years, pushing the budget into the red.
Katz also said he was uncomfortable with the idea that approving the plan would bolster the city's contention that the contract was unaffordable.
The plan calls for $50 million in overall workforce savings. The city's blue- and white-collar unions, AFSCME District Councils 33 and 47, had their contracts expire in 2009.
Butkovitz said there was "no reasonable basis" to assume the city would prevail in its appeal of the firefighters' award or that there would be "no added costs" from new D.C. 33 and 47 contracts.
He also questioned $90 million the city budgeted to pay off debt from bonds not yet issued. Those bonds, to finance needed infrastructure improvements in the final years of the plan, would add from 20 percent to 30 percent to the city's debt, Butkovitz said.
"Is it probable that a city this tightly squeezed is going to take on 20, 30 percent more in borrowing?" he asked. "If they were serious enough about doing it, wouldn't they do it right now?"
Finance Director Rob Dubow said the bonds were not "extraordinary issues."
"These are issues we do in the normal course of business to keep up with our infrastructure," he said.
The argument against budgeting for unknown wage and benefit increases is that doing so establishes a "floor" in negotiations. Butkovitz, who is required by law to review the five-year plan, acknowledged that issue and said the city ordinarily would get a pass on budgeting for increased labor costs when negotiations are starting.
Contact Troy Graham at 215-854-2730, email@example.com, or follow on Twitter @troyjgraham.