SG BESAR POLLS Dr Mahathir Mohamad today claimed the Immigration Department warned him his passport will be revoked if he criticises Prime Minister Najib Abdul Razak abroad.

"I was warned that if I say something not in support of Najib, when I come back from overseas my passport will be revoked for three years," the former premier said in his speech in Sungai Besar today.

Mahathir also disputed the Immigration Department's right to take away his travel documents.

"I didn't read this in the Federal Constitution, where this right came from I don't know."

Previously Immigration chief Sakib Kusmi had said the law empowered him to have the discretion to bar those who insult the government from leaving the country.

Mahathir was speaking at a small event attended by over 60 people, in support of Sungai Besar Amanah candidate Azhar Shukur.

After his speech, Mahathir, his wife Dr Siti Hasimah Mohd Ali, and other opposition leaders present including DAP's Lim Kit Siang signed additions to the Citizens' Declaration.

The additions are questions aimed at Putrajaya regarding 1MDB, such as who will pay if the firm loses its arbitration case with the International Petroleum Investment Co (IPIC).

Mahathir said additions regarding the National Security Council Bill may be made in the future.

The former premier said while signatures on the declaration alone were not enough to topple Najib, it may pressure the Malay rulers to act.

Asked if he would resort to street demonstrations, Mahathir said he was tempted.

"But that is not my way. You know the song 'My Way'? This is not my way," he quipped referring to the Frank Sinatra number often associated with him.

Mahathir said the government was hoping that those against them would resort to rallies as this would allow Putrajaya to arrest the protest leaders.