Delhi Police has approached the Home Ministry seeking permission to question MP Amar Singh in the 2008 cash-for-vote scam.
In a related development, MP Ashok Argal and former MP Mahavir Bhagora, who were allegedly offered money at the time of the trust vote, claimed that accused Sanjeev Saxena had told them that the money was given by the former SP leader.
Saxena, once considered close to Singh, was arrested on Sunday by Delhi Police's Crime Branch in connection with the case.
Seeking to expand its probe, Delhi Police has written a letter to the Home Ministry in which is it is understood to have asked it to approach Rajya Sabha Chairman and Lok Sabha Chairman to question Singh and Argal.
"We have sent a letter to the Home Ministry," a senior police official said.
Under the law, permission is required from the Rajya Sabha Chairman or Lok Sabha Speaker if parliamentarians are to be questioned.
Argal said, "Saxena is related to Amar Singh. Records are there (to prove it). Saxena said he brought the money from Amar Singh's place."
Bhagora also echoed Argal and alleged Saxena told him that he was coming from Singh's residence and the money was sent by him.
Argal said, "No one is above law. I will give full cooperation to the investigation".
Saxena, who is said to be close to Singh and allegedly carried the cash to the house of 3 BJP MPs to ensure that they vote in favour of UPA government in the 2008 trust vote, was arrested yesterday.
Police is also looking for a driver, Sanjay, who took Saxena to the houses of the MPs and a mobile phone used by him to make calls while delivering the cash.
Allegations were levelled by then BJP MPs Argal, Faggan Singh Kulaste and Mahavir Bhagora that Saxena had delivered Rs one crore in cash to them at the 4 Ferozshah Road residence of Ashok Argal to vote in favour of the government.
The crime branch submitted that two out of three BJP MPs -- Faggan Singh Kulaste and Mahavir Bhagora -- have stated that on July 22, 2008, Saxena delivered money to them and Argal at the latter's residence here.
Kulaste has alleged Saxena was introduced to him and Argal by Amar Singh as his secretary on July 22, 2008, according to the prosecution.
The case was registered in 2009 on the recommendation of the Parliamentary Committee.
Saxena has been booked for various offences under the Prevention of Corruption Act, police said.