Mysterious letters have been sent to people in Pennsylvania threatening to expose them if they do not vote in the upcoming primary elections.

Containing publicly available information showing whether they and their neighbours voted or not in three recent elections, the letter contains a list of 10 names and addresses of local people, including the recipients.

An updated version will be sent out after this week's election, which will see a number of officials elected into an array of public offices.

The letter does not advise residents on who to vote for.

Instead, it says: “What if your friends, your neighbours, and your community knew whether you voted?

“Why do so many people fail to vote? We’ve been talking about the problem for years, but it only seems to get worse. This year, we’re taking a new approach. We’re sending this mailing to you, your friends, your neighbours, your colleagues at work, and your community members to publicise who does and does not vote.

“This chart shows the names of the people you know and their voting histories. After the May 15th election, we intend to mail an updated chart. You and your friends, your neighbours, and other people you know will all know who voted and did not vote.”

It adds: “Do your civic duty - vote!”

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The letter is from an unknown group calling itself the Pennsylvania State Voter Program, but it does not indicate specifically who is behind the effort.

Printed on headed notepaper, this “could lead some people to believe it’s coming from an official government office,” according to LancasterOnline, a local news outlet.

All of the information it presents is on the public record, and available from the Pennsylvania Department of State for $20 (£15).

The information is frequently used by parties and candidates to examine patterns and target voters in specific areas.

Elaine Swords who along with her husband received the letters over the weekend, told Lancasteronline: “I just feel uncomfortable about the whole thing".

Although she acknowledged the information was on the public record, she said “but as far as having it sent in the mail like this, I don’t think that’s right.”

She also pointed out that some of the information in the letters appeared to be wrong. Some of the “neighbours” listed, appear to be people who live in distant towns and for the 2016 primary record, the letter states it was held in March 2016, when in fact it was held on 26 April.

This year, Democratic Governor Tom Wolf is running for his second term. The vote is uncontested, but the ballot will include three Republicans voters can choose between to challenge Mr Wolf.

Voters can also cast ballots for the state’s Lieutenant Governor, as well as for candidates for several seats in the US Senate and the House of Representatives.