Northamptonshire Police are investigating whether the posters, placed on lamp posts close to schools and polling stations, breached electoral law.
The action has been condemned by Corby and East Northants Labour candidate Beth Miller and MP Tom Pursglove, who won Thursday's election with an increased majority.
Staff members at St Patrick's RC School in Patrick Road removed some of the posters on the morning of the election and locals reported taking them down from posts in Studfall Avenue.
Speaking on Twitter on Thursday, Ms Miller said: "Political parties aren't allowed to put signs on lamp posts, especially not near polling stations.
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"Today, all around Corby, professional anti-Labour boards have been put up at polling stations and schools. Not only is it illegal it's really desperate."
Mr Pursglove said: "This categorically has nothing to do with me. Elections should be fought in the right spirit.
"I condemn this kind of behaviour."
The Polling Stations (Regulation) Bill states that it is an offence to campaign within 250m of a polling station on the day of an election.
Campaigning includes the promotion of literature associated with election candidates.
A Northamptonshire Police spokeswoman said today: "We received two reports in regard to these posters and we are currently investigating to ascertain whether any offences have been committed."