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Congress will kick off a wave of what are likely to be contentious hearings Monday on the spending habits of the General Services Administration, as lawmakers try to uncover how the agency blew through $820,000 on a Las Vegas conference.

The House Oversight and Government Reform Committee, one of four panels probing the incident, has set the first hearing for Monday afternoon. The panel has called some of the top current and former GSA officials to testify, though at least one is expected to invoke his Fifth Amendment right not to answer questions.

Lawmakers at this point are looking beyond the 2010 conference itself and into other areas where the agency may have spent money imprudently, such as on employee incentive programs. The hearing will surely fuel the controversy, which has expanded almost daily as new details emerge about the decision-making at the top levels of the GSA.

Among those on the witness list Monday are GSA Inspector General Brian Miller and former GSA Administrator Martha Johnson, who resigned in the wake of the inspector general's report on the conference.

The head of the GSA western region who organized the conference, Jeffrey Neely, has said through an attorney that he plans to plead the Fifth. His attorney says Neely doesn't need to come to D.C., but Issa insists he should appear anyway.

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"We're looking at getting to the truth and to how widespread this is. Our questions for Neely and others will have to do with not just this one event, but about the culture at the GSA and how we change it. And we believe Neely should be able to answer at least some of those questions, and we're hoping he will," Issa said.

The agency was embarrassed by a number of videos showing GSA employees flouting their spending habits. The inspector general report found thousands of dollars were spent on items like commemorative coins, expensive suites and pricey catering.

The Obama administration has condemned the conduct of the GSA officials involved. Aside from Johnson's resignation, two officials were fired and five were placed on administrative leave in the wake of the report.

Congressional sources told Fox News on Friday that the GSA's inspector general is also asking the Justice Department to probe the conference for possible criminal charges.

Fox News' Steve Centanni contributed to this report.