A window sticker saying "no political canvassers" sent out by the parliamentary office of the Welsh Secretary to all his constituents has been criticised.
A letter from Alun Cairns MP included alongside the sticker said he was giving them out free to "act as a preventative notice" to cold callers.
The sticker also discourages "uninvited traders", "charity cold callers" and "religious groups".
A spokesperson for Alun Cairns MP said the sticker was designed to give "constituents with a proven means of reducing the number of doorstep callers.”
Alun Cairns represents the Vale of Glamorgan, a marginal constituency where there were 2,190 votes between the Conservatives and Labour at the 2017 General Election.
The sticker is accompanied by a letter on House of Commons notepaper, and was sent out in an official Commons envelope.
On Twitter, some suggested it may be a breach of parliamentary standards. These state that tax-payer funded stationary for MPs should only be used "only for the performance of the member's parliamentary functions".
In the letter that accompanies the sticker, the Welsh Secretary states that "some people find cold calling a nuisance, or even an uncomfortable experience due to the potential of doorstep crime".
He also provides anecdotal evidence of stickers reducing the number of cold callers for people using the sticker from "three to four times a week to zero".
In his parliamentary constituency, candidates for other parties accused him of trying to stifle political debate.
Welsh Labour said Alun Cairns "appears to be using parliamentary resources to deter political canvassing."
Welsh Labour's candidate in the Vale of Glamorgan, Belinda Loveluck-Edwards, accused Alun Cairns of trying to "block his political opponents from speaking to voters".
She called for it to be investigated.
The Liberal Democrats’ parliamentary candidate, Sally Stephenson, said it was “another cynical attempt by the Conservatives to shut down democratic debate.”
Plaid Cymru MP Jonathan Edwards said: “Not only could this be a very serious breach of the rules, but it also shows a serious contempt for democracy. This is as stupid as it is dangerous, and Mr Cairns should seriously consider his actions".