PORTLAND, Maine — Although the referendum on the fiscal year 2014 school budget is less than a month away, the superintendent of schools said there could still be some reductions if the teachers union cooperates.

Superintendent Emmanuel Caulk said the $97.9 million budget presented to the finance committee represents the vision, values and priorities of the district.

“Next year is a very challenging budget with lots of moving parts, and as we continue to work toward building a great public school system for a world-class city, how do we organize our resources to move us forward and achieve this goal but also be fair and responsible to our taxpayers?” he said.

As it stands, the budget will cause an increase of more than 3.5 percent in the school’s portion of the tax rate, Caulk said.

“There were some very difficult and painful decisions made [during the process of crafting the budget],” he said.

Since he presented the original budget on March 12, the superintendent said more than $1.5 million in cuts have been made, including the reduction of 50 jobs across the district, adding furlough days and cutting funding for supplies.

Caulk said that everyone in the district is working to ensure the reductions in the budget do not affect students on a day-to-day basis. He said he will take five furlough days next year, and is asking all nonunion employees to “invest” in the plan.

“In some areas we were able to get our employees to invest and share in the solution,” he said. “I would hope that all employees would make a similar investment and put our students first and share in the solution.”

Budget documents for the district show that 69 percent of this year’s budget is made up of labor costs, including a 5 percent pay raise for teachers, custodians, secretaries and bus drivers, and 4 percent for principals.

Unions representing the principals, custodians and secretaries have submitted to some proposed changes, including the addition of furlough days, Caulk said, but the largest of the three unions, the teachers union, has been unwilling to negotiate on their contract.

Caulk said the solution is not that easy when it comes to dealing with the teachers union because they are in the middle of a three-year contract.

“I think we have some of the best teachers in the state, certainly in Cumberland County. They do a terrific job each day,” he said. “I know that our teachers union has been there for the district in the past, and although right now we are still bound by the contract, I am hopeful that they would share in the solution as we move forward with such a difficult budget.”

He said that the unforeseen costs of having to take on $1 million in curtailment this year and potentially $1.5 million in retirement costs next year has made the process of crafting the current budget difficult.

The addition of Baxter Academy for Technology and Science also poses a challenge, Caulk said, because around $600,000 may have to be shifted to the charter school to support Portland students attending the school.

He said these factors were not on the radar two years ago when the teachers contract was signed, but he is hopeful that continued lobbying of the Legislature will lead to the removal of the teacher retirement shift.

Caulk repeated a previous call for the teachers union to work with the district, and asked that all employees make the same investment in the district.

“Our unions have been with us in helping us think through some nonlabor reductions, but at this time they have not offered any changes in their current contract and we are bound by the contract,” the school chief said.

Representatives from the Portland Education Association did not respond to telephone calls seeking comment.

The final School Department budget will be before the City Council on May 6 and voters will have their say on the $97.9 million spending plan in a referendum on May 14.