Gov. Nathan Deal has warned key lawmakers that he will order them into special session if they fail to pass what he considers to be an adequate transportation funding bill by the time the regular session ends next Thursday, The Atlanta Journal-Constitution has learned.

Three individuals with knowledge of the negotiations, who were not authorized to speak on the record, said Deal has made it clear he will use his power to order lawmakers back to Atlanta if they fail to pass House Bill 170 or if he determines it does not raise enough money for transportation.

“He has told staff to avoid scheduling vacations the last week of June,” Deal spokesman Brian Robinson said. “And he has told legislators that’s a possibility.”

The General Assembly has not returned to Atlanta for a special session since 2011, when it met to redraw their district maps following the 2010 census.

HB 170 is currently before a conference committee of three House members and three senators who are searching for a compromise. The two chambers have passed greatly different versions of the bill, although both would eliminate state sales taxes on motor fuel and create one per-gallon excise tax. The House version was set at 29.2 cents per gallon for gasoline and 33 cents per gallon for diesel; the Senate adopted 24 cents, along with a $5-a-day fee on rental cars.

Much of the discussion about a potential compromise has centered on getting the Senate to agree to a higher excise tax and eliminate the rental car fee, which would cost state government — a regular renter of cars — an estimated $2.5 million a year.

But Senate Transportation Committee Chairman Tommie Williams, R-Lyons, said that's unlikely to happen.

"I see no way we can get to 29 cents," Williams said, noting that HB 170 passed the Senate with no room to spare after Democrats unanimously opposed the bill.