Referring to the seizure of voter ID cards, Modi said people will not forgive Congress' "attempt" to win elections by "using" bogus ID cards.
"Making multiple fake voter ID Cards to win elections is a tactic of Congress. People should never forgive such a party. Fearing a crushing defeat, Congress is indulging in all kinds of malpractices," Modi told a public gathering in Chikkamagaluru.
The state's Chief Electoral Officer (CEO) Sanjiv Kumar late Tuesday night said 9,746 voter cards were seized from a flat in Raja Rajeshwari Nagar.
Both Congress and BJP claimed the flat belonged to a woman associated with the rival party.
Union minister Prakash Javadekar has alleged Congress candidate and sitting MLA Munirathna Naidu was behind the alleged racket.
Congress communication in-charge Rajdeep Singh Surjewala has claimed that the flat owner Manjula Nanjamari is associated with the BJP.
Karnataka Chief Minister Siddaramaiah refused to comment on the issue, saying he didn't know anything about it.
"I don't know anything about this, there is Election Commission to look into it," he said.
Meanwhile, the BJP demanded countermanding of polls in Raja Rajeshwari Nagar Assembly constituency.