Mayor Rahm Emanuel has long said a property tax increase for Chicago residents is the “last resort” to cover a scheduled increase in payments owed to the city’s cash-strapped police and fire pensions.

To avoid a hike, he’s asking Illinois state legislators to approve changes to the funding schedule for those two retirement funds - in addition to adding future payments to the pensions from a new source of revenue created by a potential new, city-owned casino.

Emanuel’s administration says that a 5-year-old state law forces the city to pay an extra $600 million this year toward its cash-strapped retirement funds for police officers and firefighters.

Those pensions are severely under-funded, so Emanuel wants lawmakers to pass a bill that would put off those payments for a few years - in exchange for later adding larger payments and putting the pensions on a better funding schedule over the next 40 years, rather than the current 25-year plan.

Under the extended schedule, the pensions would be funded at 90 percent in 2055, rather than the current rates of around 25 percent funded. If the bill is not passed, said Steve Koch, Emanuel’s deputy mayor, then property taxes could skyrocket.

“I think this is always a matter of, in this sort of situation, of trying to reach a medium,” Koch explained, “where you protect the funds, which has been an objective of ours and an objective of the mayor since he took office, and equally protect taxpayers.”

But Republicans criticized Emanuel’s plan, saying the mayor’s office is in a “fantasyland,” — because the bill says it would take money from a Chicago casino, or casinos, to pay for pensions. Casinos that, as of yet, have not been approved by state lawmakers.

“You’re essentially in a fantasyland here, assuming that you’re going to get a casino and all the revenue associated with that casino, with us not even seeing a bill that relates to that,” said State Rep. Jeanne Ives (R-Wheaton).

Lawmakers have been negotiating a gambling expansion bill behind closed doors, which could include a city-run casino; but so far a compromise has not been introduced to lawmakers. Koch said that if a casino is not approved, then the city would rely on cuts to city services or increases in fees or revenues to pay for the administration’s proposed pension bill.

Meantime, the union representing Chicago firefighters, support the administration’s pension plan, unlike other labor unions raising recent court challenges over previous efforts to change other city and state funds

“We’ve been pretty conservative with our benefits over the years, so we don’t pull no shenanigans in our fund,” said Dan Fabrizio, with the Chicago Firefighters Union.

The measure was approved by the House and Senate with mostly Democratic support. Gov. Bruce Rauner’s office has not commented on his position on the bill.

Tony Arnold is WBEZ’s Illinois state politics reporter. Follow him @tonyjarnold.