The Bernie Sanders campaign is claiming that Hillary Clinton is “infiltrating” Monday’s Iowa caucus with paid out-of-state workers in a last-ditch effort to mobilize pro-Clinton voters.

Sanders’ campaign manager, Jeff Weaver, said that the Clinton campaign is “infiltrating the caucuses with out-of-state paid staffers,” according to Yahoo News.

Weaver cited a letter that a Sanders supporter in Hawarden, Iowa, received from the Clinton campaign that named a man named Morgan Luther as the Clinton precinct captain, even though Luther is not a resident of the state of Iowa.

“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,” the man who received the letter told Yahoo News.

Using out-of-state precinct captains is not against the rules.

Clinton is running neck-in-neck in Iowa with Sanders, who has pulled to within the margin of error in both the Iowa State University/WHO-HD poll and also the final Des Moines Register poll.

Sanders held a concert Saturday night in the college town of Iowa City with the band ‘Vampire Weekend.’ Bill Clinton was in Iowa City Sunday at a smaller event.