Four Parliamentarians whose names have figured in the Babubhai Katara human trafficking case are likely to be questioned by the police on Tuesday as part of their investigations into the emigration racket.

The police had issued notices to the MPs on Monday, after their names came up during the interrogation of Sunder Lal Yadav, an alleged conduit in the high profile case.

The MPs who have been summoned by the police for questioning are BJP's Ramswarup Koli and BSP's Mitrasen Yadav, Mohammad Tahir Khan and Ashok Kumar Rawat.

However, Khan is unlikely to appear as he has expressed his disability to spare time because of elections in Uttar Pradesh.

Investigators would like to know about their travels abroad and whether anybody had accompanied them.

The MPs will have to explain why their names were taken by a person arrested in a human trafficking case, a senior police official said.

Though the Delhi police maintains that the MPs have been asked to help in the investigation, sources said the investigators will grill them to know whether they knew Yadav or any others arrested in the case so far.

The MPs have been asked to bring their passports as police wants to 'physically verify' the travel document.

"This would help us in finding out about their visits abroad," a senior Crime Branch officer said.

The police have so far arrested six persons, including Katara and his aide Rajender Kumar Gampa in the case after the Dahod MP was nabbed at the international airport last Wednesday while trying to smuggle a woman and a teenaged boy out of the country in his wife and son's passports.