The Bharatiya Janata Party is inquiring into the absence of its nearly 20 MPs from the Lok Sabha during the voting on Tuesday on the introduction of the bill for simultaneous elections.
As the party had issued a whip asking all its members to be present in the House, the absence of so many MPs has irked its leadership, sources said.
However, they added that a number of MPs had informed in advance about their absence due to various personal and work-related reasons.
"We are definitely looking into the reasons behind their absence. Quite a few had genuine reasons," a senior leader said.
Some MPs, including Union minister C R Patil, were engaged with Prime Minister Narendra Modi's public event in Rajasthan, the sources said.
Four to five MPs from BJP allies were also not present during the voting, they said, adding that this is also being looked into.
Two bills that lay down the mechanism to hold simultaneous elections were introduced in the Lok Sabha after a fiery 90-minute debate on Tuesday.
The opposition alleged that the move was "dictatorial" and impinged on states' powers even as Law Minister Arjun Ram Meghwal refuted such concerns.
The Constitution (129th Amendment) Bill was introduced in the Lok Sabha by Meghwal after a division of votes.
As many as 269 members voted in favour of the Bill and 198 against it.
