In the latest attempt to crack down on potentially embarrassing digital leaks from presidential fundraisers, President Barack Obama's campaign has begun asking donors attending small fundraisers with the president to turn over their cell phones before entering.

Pool reporter David Nakamura of the Washington Post reported that at a $35,800 a head fundraiser at the home of Blackstone COO Hamilton “Tony” James in New York City Monday night, the 60 attendees were asked to place their phones in plastic bags by the door.

An Obama aide called the move it "standard operating procedure," but veterans of a range of other campaigns said they'd never heard of the practice, which is common in secure White House spaces where there are concerns of espionage, but unknown in contexts in which only political secrets are discussed. The new prevalence of sophisticated audio and recording capacities in mobile devices owned by virtually anyone wealthy enough to write a check to a political campaign, however, has put a new pressure on campaigns concerned with staying on a public message.

The fundraising sessions are one of the last vestige of privacy for the president outside of the White House, and a rare opportunity for top donors to hear relatively unscripted remarks by the most powerful man in the world, and to ask him questions. Obama's prepared remarks at the events are open press and covered by a small group of reporters, but the "press pool" is escorted out of the room before the Q&A period.

At Romney fundraisers, attendees are greeted to signs of "Please, no audio or video recording," and like Obama events, larger fundraisers are open to reporters; a Romney spokesperson, however, told BuzzFeed that their campaign allows donors to keep their phones during fundraisers.

Former aides to presidential candidates Hillary Clinton, Rick Perry, and Jon Huntsman all expressed surprise at the practice, and they've never seen an instance where a campaign asked donors to surrender their cell phones.

The former Clinton aide called the Obama policy "absurd," suggesting that the Obama policy is almost certainly a response to the infamous 2008 fundraiser where Obama described voters in rural Pennsylvania as "bitter."

"They cling to guns or religion or antipathy to people who aren’t like them or anti-immigrant sentiment or anti-trade sentiment as a way to explain their frustrations,” Obama told donors in San Francisco, in a gaffe that breathed new life into Clinton's campaign at the time.

"What is he hiding? Candidates should be for and against the same issue in private as they are in public," said former Perry campaign manager Rob Johnson. "This shows just how uncomfortable the Obama team is with their message an their candidate. And in addition to religion and guns, voters like to cling to their cell phones."

A spokesman for the Secret Service confirmed that the ban was not put in place at their request.

[This story has been updated with the Romney campaign's position and with comment from the Secret Service.]