CHICAGO (CBS) — Aldermen have delayed action on a proposed ordinance that would require many gas stations to offer fuel that contains a higher blend of ethanol, in an issue that has Mayor Rahm Emanuel and powerful Ald. Ed Burke (14th) at odds.

Several aldermen teamed up to defer a full City Council vote on requiring about 25 percent of stations in the city to equip at least one pump to carry so-called E15 fuel, which is 15 percent ethanol, compared to 10 percent in most other gasoline.

After the meeting, the mayor told reporters the whole proposal needs work.

“Before we take a step like that, I think this ordinance needs a little more time to be thought through, and done in a way that doesn’t put undue burdens on the small businesses, but also makes sure that our goal as a city – and from an environmental policy – is also met,” Emanuel said.

Burke, who chairs the Finance Committee which backed the ordinance he sponsored earlier this week, bristled at the mayor’s comments.

“Well, we’ve been studying it for quite a while, and I think that – in terms of small businesses – there’s only about 100 filling stations that would be affected by the law, with the amendments we adopted,” he said.

Opponents have said few cars on the road can use E15, which can damage older model vehicles if owners pump it without realizing they are using the higher blend of ethanol.

The AAA has said more than 90 percent of all cars on the road have not been approved by manufacturers to use E15, and the blend should only be used by vehicles with “flex fuel” engines, even though the U.S. Environmental Protection Agency has approved E15 for use in cars manufactured since 2001.

At the committee hearing on the ethanol ordinance on Monday, gas station owner Rollie King said it could cost him more than $50,000 to replace pumps at his stations.

Gas stations that sell fewer than 500,000 gallons of gasoline a year, or those with underground storage tanks incompatible with E15 blend gasoline, would be exempt from the mandate. No stations would be barred from continuing to sell a 10 percent blend.

Thomas Buis, CEO of Growth Energy, which represents ethanol producers, said claims of high costs to convert pumps to E15 are nothing but a scare tactic to drive up the cost.

“There’s a group called the Petroleum Equipment Institute that estimates that the average cost would be about $1,000,” Buis said earlier this year.

Burke insisted the ethanol ordinance is not dead.