NEW DELHI: Election Commission has instructed presiding officers of all polling stations in West Bengal to check electronic voting machines (EVMs) and ensure that all candidate buttons on them are clearly visible to the voter, with not a single button covered with tape, glue or any other material.“No colour, ink, perfume or any other chemical can be put on the candidate button of the ballot unit,” EC told presiding officers. While EVM buttons masked with tape, etc., prevent voters from making an informed choice, buttons laced with colour or perfume, when pressed, leave a trail on the voter’s finger, making it easy for party supporters and anti-social elements backed by the party to detect the candidate they may have voted for, thus violating the secrecy of the ballot.EC sources told TOI on Wednesday that in the event of such malpractices — commonly reported during the previous polls in West Bengal — coming to light, the commission shall treat them as tampering with or interfering with the EVM, which is an electoral offence.“The Election Commission will not hesitate in initiating criminal action in such cases, by ordering the registration of an FIR, and also order a repoll in the polling station concerned,” said an official.