The tax was increased by 150 percent for residents and 60 percent for businesses starting in fiscal 2011. The increase is set to expire on June 30, the end of the current fiscal year.
The increase brought in $110 million in additional revenue in fiscal 2011 and is expected to bring in about as much this year -- money that supports services residents can't afford to lose, the county's union leaders wrote in a letter to newly elected County Council President Roger Berliner, D-Bethesda.
The letter was signed by the heads of the county's police, fire, teachers, principals and county government employee unions.
"The county is not in a position to sacrifice that amount in any way," said Gino Renne, president of the Municipal and County Government Employees Organization.
Montgomery is facing a potential $140 million hole in next year's budget, according to Office of Management and Budget Director Jennifer Hughes.
As a result, county lawmakers likely will agree with Renne when the spring's budget process arrives, Berliner said Thursday.
"The county executive has already indicated that he will send over a budget with a continuation of the energy tax," he said. "If that's what he sends over to us ... it will be very difficult to come up with savings of that magnitude in addition to the hole that we're already in."
Whether the tax increase expires means choosing between more budget cutbacks or improving revenue levels, County Executive Ike Leggett told the County Council in September.
Though Leggett has not made a decision, according to spokesman Patrick Lacefield, the sunset would cost the county a large amount of revenue and could mean the difference between, for example, giving government employees raises for the first time in four years and another freeze.
"We've not been able to do anything on compensation in a few years, and that concerns the county executive," Lacefield said. The county is renegotiating several union contracts, and the results of those negotiations -- including pay raises -- will affect Leggett's budget proposals in March.
Schools Superintendent Joshua Starr also is also asking for raises for public school teachers and other employees.
The unions don't want to extend the tax increase -- they want to eliminate the bill's sunset outright, meaning it would be in place unless repealed.
The tax is the only one the county can levy on federal agencies, the unions wrote in their letter.
"Everyone's already paying the energy tax," said Montgomery County Education Association President Doug Prouty. "It's not an increase in taxes at all."