Higher Education Minister William Ruto, the de facto leader of the No campaign, tops a list of politicians in his camp accused of hate speech.
National Cohesion and Integration Commission on Monday said it had adverse evidence of on Mr Ruto, an assistant minister and four MPs.
The commission also said it had written to President Kibaki and Prime Minister Raila Odinga urging them to suspend all campaigns until July 13.
Last month, the Interim Independent Electoral Commission announced that the official campaign period for the referendum would start on July 13 and end on August 2 — two days before the vote.
The commission’s chairman, Dr Mzalendo Kibunjia said his team had evidence against Mr Ruto, Roads assistant minister Dr Wilfred Machage and MPs Mr Fred Kapondi, Dr Julius Kones, Mr Mohammed Sheikh Dor and Mr Joshua Kutuny.
Also on the list is a political activist operating in Nairobi and Githunguri, Ms Christine Nyangitha. Dr Kibunjia said the evidence had been handed over to the CID for further investigations.
“We worked closely with the police and based on the substantial evidence, we have issued summons to the said persons and requested the security agencies to investigate with a view to prosecution,” Dr Kibunjia said.
But Mr Ruto accused the Yes team of using the National Cohesion and Integration Commission to intimidate critics of the proposed constitution.
“I understand today, they have summoned me to their offices. I will go there tomorrow and listen to their allegations against me,” he said.
He warned the commission that they risked losing their credibility if they allowed themselves to be used by the government to demonise the Red side.
Those found guilty of hate speech risk being fined Sh1 million or to serve a prison term not exceeding five years or both.
The National Cohesion and Integration Act allows the commission to seek the help of the courts if a person fails to heed its summons. The summons comes a day after six people were killed at a No rally at Uhuru Park.