VASSALBORO — Town voters will be asked Thursday to approve a $6.6 million school budget that was mistakenly left off the primary election ballot two weeks ago.

Town and school officials say they want to make sure voters are aware of the special election because of a town ordinance that requires at least 125 people to vote for it to be a valid election.

There were 542 municipal ballots cast at the June 12 primary election, which included a selectman’s race and one school committee seat, according to results provided by the town.

“We really need their help,” said Town Manager Mary Sabins.

On the afternoon of election day, Sabins discovered that the school budget validation question was left off town ballots. Later that same week, selectmen held an emergency meeting to set a date for a new election. The new budget year starts July 1.

Polls will be open at the town office from 8 a.m. to 8 p.m. Thursday.

Sabins estimated that it will cost a “couple hundred” dollars to hold the special election.

Vassalboro is part of Alternative Organizational Structure 92, which includes Waterville and Winslow. Voters in each municipality approve or reject school budgets in separate votes.

At the annual town meeting on June 11, there were few questions about the school budget, which is lower than the current spending plan but will result in a tax increase because of less state funding. It’s estimated the budget will increase taxes by $1 per $1,000 of property valuation, which will change the rate from $10 to $11.

Superintendent Eric Haley said the town is getting $467,146 less in state funding. He said he was “pleasantly surprised” that those who attended town meeting seemed to understand that it wasn’t increased spending that is driving up the tax rate.

“Because town meeting went as smoothly as it did, I think it’s going to pass,” he said.

In a separate action, the $1.7 million town budget was approved by voters at the town meeting.