"The campaigning strategy of some candidates is in fact humiliating and insulting to the people," the hardline incumbent said, quoted by Iran's state radio.
"How do you allow yourselves to abuse the freedom which the people have given you?" asked the president, who is running for re-election on June 12.
"If the insults to the nation continue, the government will reconsider its approach," he said, noting the government had not yet "shut down even one newspaper in the face of accusations and insults."
Ahmadinejad has come under fire from all three of his election rivals, mainly over his handling of the economy. He stands accused of stoking inflation and wasting Iran's windfall oil revenues.
His rivals are moderate war-time premier Mir Hossein Mousavi, reformist cleric Mehdi Karroubi and a former head of the Revolutionary Guards, Mohsen Rezai, a veteran conservative.
