NEW DELHI: The Election Commission has instructed presiding officers of all booths, particularly in West Bengal, to check and ensure that all candidate buttons on electronic voting machines (EVMs) are clearly visible and not covered with tape, glue or any other material, including colour, ink, perfume or chemical that can compromise the secrecy of votes.Cases in which candidate buttons are found with the above anomalies are likely to fall under tampering or interference with electronic voting machines (EVM), which is an electoral offence.EC officials on Tuesday said the commission will not hesitate to take criminal action or order a repoll in such cases.Wherever instances of tampering are noticed, the presiding officer will immediately inform the sector officer or returning officer.