CBI sources said they have already questioned his personal staff in connection with the case and Paswan might be summoned after the elections.
The role of Paswan has come under the scanner of the agency following recovery of some documents which, agency sources claimed, indicate that his staff may have been actively involved in extending favours to some candidates.
Paswan has denied allegations.
In January, CBI had registered two separate cases related to alleged irregularities in the appointments in the middle and junior management level in the public sector undertaking in 2008 in which a former Executive Director of the plant and other former senior officers have also been named as accused.
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Paswan was Union minister for chemicals, fertilizers and steel during the UPA government between May 2004 and May 2009 and these allegedly fraudulent appointments were made during his tenure.
"Such actions cannot be taken at the level of lower rung staff without the approval of the minister concerned. We may question him (Paswan) in this connection. A final decision when the questioning would take place may be taken as the probe progresses," a senior CBI official said.