Democratic presidential candidate Bernie Sanders's campaign staffers are demanding wages of at least $15 hourly, but a campaign strategist is calling that prospect "ridiculous," saying productivity would have to be cut to stay within budget.After facing criticism earlier in July, the Vermont senator defended how he compensates his staff."I'm very proud to be the first presidential candidate to recognize a union and negotiate a union contract," he told the Des Moines Register on Friday. "And that contract was ratified by the employees of the campaign, and it not only provides pay of at least $15 an hour, it also provides, I think, the best health care benefits that any employer can provide for our field organizers."Sanders's campaign manager Faiz Shakir said as negotiations continue, the campaign would be "limiting hours," he told Newsweek."We look forward to continuing those discussions and obviously are disappointed that some individuals decided to damage the integrity of these efforts before they were concluded," he said. "As these discussions continue, we are limiting hours so no employee is receiving less than $15 for any hours worked."Republican strategist and campaign manager Joe Desilets told the Daily Caller News Foundation that less than $15 hourly is relatively well-paid for certain positions.He said $13 hourly is "probably on the high end of standard."