Keighley MP Ann Cryer has been accused of wasting taxpayers' money to write to her constituents.
Prospective Conservative parliamentary candidate Karl Poulsen has made the claims after he was alerted to a letter inviting people to a coffee morning.
Mr Poulsen claimed the invitation - written on House of Commons stationery and franked in the Commons - should have been paid for through party funds.
But a spokesman for the MP indicated an election had not been called and the letter was part of Mrs Cryer's duties as an MP.
Mr Poulsen was informed of the letter while campaigning. He said he was aware of at least a dozen such letters, inviting people to a coffee morning and advice surgery at Oakworth last week.
He said: "The sin is using the paid-for envelope here. You can only use paid-for stationery to reply to constituents.
"This is clearly -- in the run-up to the general election -- a flagrant abuse of taxpayers' money."
Mr Poulsen added: "I have no problem with the Labour Party contacting people. We are doing it. But we are putting our hands in our pockets to contact people."
He believed names and addresses had been taken off the electoral register.
Mr Poulsen is preparing to make an official complaint to Parliament's Serjeant-at-Arms, who is responsible for policing MPs, when the House returns from its Easter break.
A spokesman for Mrs Cryer said taxpayers' money could be used for all matters relating to constituents, such as staff, website, office space and letters.
He added the only other way people could meet their MP to raise concerns was to visit Mrs Cryer in Westminster.
Mrs Cryer said: "I do not think that the Tory candidate has realised that a general election has not been called and that I am the Member of Parliament with a job to do. It is very clear that he has no idea what representing people is about. Inviting constituents to discuss issues over a cup of coffee is part and parcel of a process that I have continued over the last eight years."
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