The Chicago Transit Authority is threatening to reduce some suburban bus service if several Cook County commissioners follow through with a plan to cut $1.3 million in county funding to the agency.

The proposal filed this week could set up a showdown between County Board President Toni Preckwinkle and the City of Chicago over how much money each government should chip in for CTA service.

Just days before the CTA is set to present its 2012 budget proposal to the Cook County Board of Commissioners, a bipartisan group of four board members introduced a non-binding resolution Thursday proposing the county reduce the amount of gas tax revenue it turns over to the CTA each year to $675,000, from $2 million.

Citing the county’s projected $315 million budget deficit for 2012, the commissioners urged Preckwinkle to offer less money to the CTA next year. Cook County should be paying less for the suburban service it receives, based upon ridership, according to the resolution.

“The CTA primarily serves city residents and we are looking at potential options that would allow us to allocate funds for the benefit of all County residents,” said Jessey Neves, a spokeswoman Preckwinkle.

But for the CTA, the stakes could be much higher than a relatively small $1.3 million funding cut: At risk is about $128 milion in discretionary money that the agency receives from the Regional Transportation Authority, which oversees all Chicago-area transit agencies. State law stipulates that the RTA can’t dole out that discretionary money unless the CTA receives a combined $5 million in support from both Chicago and Cook County, RTA Executive Director Joe Costello said in a statement to WBEZ.

That could turn up the pressure on the city to contribute more, even as it copes with its own budget problems. 

“This resolution would violate a 30-year-old compact between the city, county and state to support mass transit in the region,” CTA spokesman Brian Steele said in a statement to WBEZ Friday. “Reducing this funding could possibly lead to some reduction of bus service in suburban Cook County.”

The CTA serves 40 suburbs. Agency representatives will show up to Tuesday’s County Board meeting to make their opinion known, Steele said.

Chicago Mayor Rahm Emanuel’s office did not respond to requests for comment.

The board members maintain that while the county has traditionally handed over the money to the CTA, the transfer isn’t required by state law. The resolution is sponsored by Commissioners Joan Patricia Murphy, D-Crestwood; Peter Silvestri, R-Chicago; Deborah Sims, D-Chicago; and Jeffrey Tobolski, D-LaGrange.

None of the commissioners responded to interview requests Friday.