Bernie Sanders campaigns in Cedar Rapids, Iowa, on Jan. 30. (Photo: Dennis Van Tine/Star Max/IPx via AP)

WEST DES MOINES, IOWA — Jeff Weaver, the presidential campaign manager for Sen. Bernie Sanders, D-Vt., says he is worried Hillary Clinton’s team is resorting to “irregular” tactics to win the Iowa caucus on Feb. 1.

Weaver’s concern is based on what he described as an “alarming” letter received by a voter named Dennis Clifford in Hawarden, Iowa. Although Clifford is a Sanders supporter, the letter, from a Clinton campaign office in Sioux City, urged him to caucus for Clinton and identified a non-resident as his local precinct captain. That would not actually be prohibited, but Weaver, who admitted he wasn’t familiar with the rules, claimed it indicated the Clinton campaign is “infiltrating the caucuses with out-of-state paid staffers.”

Clifford, a retiree, told Yahoo about the letter, which he received earlier this month. It was written by a Clinton campaign staffer named Morgan Luther, who was identified as the precinct captain for Hawarden.

“I’m Hillary’s captain for your caucus and you’ll find me at your caucus wearing a blue shirt that says ‘captain,’” Luther wrote. “It’s my job to make sure all of Hillary’s supporters are in attendance on caucus night to ensure Hillary wins.”

According to Clifford, he became concerned when he realized that the return address on the letter was a Clinton campaign office in Sioux City, Iowa, which is about 50 miles away from Hawarden. Clifford said he found it unusual that any campaign would name someone a precinct captain who was not from the precinct.

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“Coming from Sioux City into the Hawarden caucus and trying to influence the voters in the Hawarden caucus, I don’t know what the rules are, but it certainly is irregular,” Clifford said.

Luther is working for the Clinton campaign in Iowa although he is not a resident of the state. The Sanders campaign said the letter raised suspicions that the Clinton campaign is packing the caucuses with out-of-state voters.

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“I think this raises a very serious concern that they’re infiltrating the caucuses with out-of-state paid staffers,” Weaver said. I would hope that the media will be able to get to the bottom of this before Iowans go to the caucuses on Monday night.”

Weaver stressed that he’s not concerned about the campaign using staffers in Iowa that are not from the state. Both campaigns have staffers in Iowa who are not from there. Rather, Weaver fretted about the possibility they are having non-residents attempt to participate and be counted in the caucus.

“People who are in the caucuses are supposed to be Iowa voters. … Of course we have out-of-state staff. I’m here in Iowa right now and, you know, I don’t live in Iowa,” Weaver said. “But I’m not going to the caucuses either to participate. I’m not trying to participate in the caucuses.”

Democratic presidential candidate Hillary Clinton speaks at a rally at Abraham Lincoln High School in Des Moines, Iowa, on Jan. 31. (Photo: Andrew Harnik/AP)

Luther’s letter is not actually evidence the Clinton campaign broke any rules. Precinct captain is a title campaigns have created as part of their organizational efforts to get voters to caucus. It is not an official position. While people who are not residents are not allowed to participate and be counted in a precinct’s caucus, anyone is allowed to attend and watch. In fact, the Clinton campaign claims to have a 17-year-old volunteer — too young to participate — serving as a captain in one precinct.

While it would not necessarily be against the rules for a precinct captain to come from outside of Iowa, it could offend some Iowa voters.

The Clinton campaign maintains all of its precinct captains are Iowans. When Yahoo asked about the letter, a spokesperson for the Clinton campaign claimed their precinct captain in Hawarden, confirmed as of Jan. 25, is a woman from Iowa named Angeline Joy, not Luther. In cases where a precinct captain was not confirmed, the Clinton campaign spokesperson claimed letters to supporters have identified local staffers as “captains” in the interim.

Weaver said he was unaware of whether regulations require precinct captains to be residents, but still has concerns about Luther’s letter. He said he has not heard of any other indication the Clinton campaign has someone from out of state serving as a precinct captain.

“You’d have to talk to the party or somebody else about it. I don’t know the answer to that,” Weaver said when asked about the rules. “I do know that, certainly on its face, it seems highly suspect to have out-of-state paid staffers participating.”

The Clinton campaign said none of its out-of-state staffers will attempt to participate in the caucus.

As Sanders has emerged as a surprisingly strong opponent to Clinton, his team has levied several accusations against her campaign. The Sanders campaign has questioned whether the Democratic National Committee has unfairly coordinated with Clinton, who remains the frontrunner. In recent days, the two camps have argued back and forth about the debate schedule. Sanders has charged his opponent is trying to avoid giving him additional exposure by scheduling more debates.

This is not the first time a campaign has been accused of bringing non-residents to Iowa ahead of the caucus. During Clinton’s unsuccessful 2008 presidential bid, her staff charged Barack Obama’s team was “systematically trying to manipulate the Iowa caucuses with out-of-state people.” In light of the disputed letter, Weaver said it was “ironic that the Clinton campaign in the past has suggested that President Obama somehow packed the 2008 caucus with out-of-state people.”