John McCain is reevaluating his entire campaign staff, FOX News has confirmed, and his campaign has issued a new conflict-of-interest policy following revelations that several advisers were engaged in lobbying work for entities he's spoken out against.

Under the policy, nobody on the campaign can be a registered lobbyist or receive payment for such work. Nobody with a campaign title may work with a "527" group or other independent group that publicly supports or opposes a presidential candidate.

The campaign is requiring all staff members to fill out a questionnaire disclosing all previous lobbying employers and clients, especially those that could be "embarrassing for the senator and the campaign."

The policy was released publicly after The Politico reported Thursday that McCain adviser Craig Shirley was asked to leave the campaign following inquiries about his work with a "527″ group that sharply criticized the Democratic presidential candidates.

The 527s, named for the part of the tax code that regulates them, are independent special interest groups formed mainly to influence elections.

Shirley was advising McCain while his firm also was doing public relations work for the group Stop Her Now, according to the article. The Stop Her Now group initially targeted Hillary Clinton -- in part through cartoons and animated features on its Web site -- but has changed its message to "Stop Him Now," going after Barack Obama as he's taken the lead in the Democratic contest.

Shirley was ousted after two other high-profile McCain aides resigned their positions following reports that they were working for a firm that lobbied for the Burmese military junta in 2002.

One of the two was Doug Goodyear, the man picked by McCain's campaign to run the 2008 Republican National Convention. A Newsweek story scrutinizing Goodyear and his firm DCI Group's $348,000 contract with the junta also drew attention to DCI's work with 527 groups. Goodyear then stepped down from his convention role "so as not to become a distraction in this campaign."

Under McCain's new policy, even part-time volunteers are being required to disclose any lobbyist status and are prohibited from dealing with any policy decisions related to their work as lobbyists.