LAFAYETTE -- Lafayette Unified School District leaders are hammering out the language of a potential school tax measure that could go before voters in May.

If greenlighted by the governing board, the parcel tax measure will ask residents to contribute $539 to the school district each year beginning July 1, 2015. The tax would include a cost-of-living adjustment for inflation carried over from a previous parcel tax, and an exemption for seniors ages 65 and over, according to proposed ballot language.

Unlike previous measures, this parcel tax would not sunset.

Board members are scheduled to vote Jan. 27 on the final language and whether to place the measure on the ballot.

The proposed tax combines two existing parcel taxes set to expire June 30, 2015. Voters decided in 2007 to pass Measure J, which increased a $132-per-parcel tax to $313 with an annual 3 percent inflation increase. They approved the $176 Measure B tax in 2011.

Administrators say the loss of those funds will be a blow to the district, as the taxes generate about $4.8 million -- 15 percent of its annual budget.

"We know that losing the existing parcel taxes would be devastating ... to our budget and to our programs," said school board President Teresa Gerringer at a meeting Jan. 16. "We would have to make huge cuts."

Those reductions could include scaling back professional development training for teachers, classroom support staffing and possibly increasing class sizes.

If voters embrace the prospective tax, the funds would continue to pay for core academic programs including math, science and technology, said district Superintendent Rachel Zinn.

"We absolutely need the $4.8 million from the parcel tax," she said.

A poll conducted late last year revealed that 77 percent of voters surveyed said they would support extending the existing parcel taxes without a rate increase.

The district has been coping with the fallout of what Zinn said was a serious budget crisis resulting from cuts and losses of state funding. To cope, the district has cut custodial, administrative and other support services and reduced some instructional aide time.

It's also facing a $5.6 million state funding gap projected next fiscal year.

At a recent district school board meeting, chief business official Lenee Cadotte told officials that state funding under Gov. Jerry Brown's new funding formula would contribute about $923,000 to that funding gap.

Calotte said Lafayette's state aid funds are not as much as other districts because of the city's high property tax base.

The district also has very small numbers of specific targeted populations that receive increased funding, Zinn said.

The school district expects to end the current fiscal year with a $710,644 shortfall and a general fund ending balance of $4.82 million.