Cablevision Systems Corp. is raising prices on its high speed Internet service by $5 a month, starting next year, in what it says is its first such increase in a decade.

The Long Island, N.Y.-based cable operator said the new price would add an average of 3.2% to broadband customers' monthly bills. It will affect customers who take the "triple play" package of television, broadband and phone, but not those who are currently paying discounted promotional prices. Customers on promotional packages will pay the increase when their...