The use of “robo calls” to influence voters on the Regional School Unit 18 budget referendum may be unusual, but there’s nothing illegal about them, state officials say.

Budget opponents who helped reject the $32.6 million budget won’t release information about who organized the calls and how much money was spent on them.

Superintendent Gary Smith said he was surprised to hear that voters had received calls from computerized phone banks with recorded messages urging them to vote against the budget. Typically, they are used only in larger elections, by well-funded and well-organized campaigns.

“I have dealt with a lot of tough budgets,” Smith said. “This approach was very new.”

There’s no way to tell how many voters were influenced by the calls. In all, 1,862 — just 13.65 percent — of the district’s 13,637 registered voters voted in the referendum.

Sidney Selectwoman Kelly Couture said the budget’s opponents paid for four 30-second recordings to be sent to phone numbers in the district towns of Belgrade, China, Oakland, Rome and Sidney.

Couture said she provided the voice for two calls, which she recorded by reading a script into an Internet-based interface.