Robert J. Halderman, the producer suspected of blackmailing Letterman for $2 million to keep the TV host's affairs with co-workers quiet, is expected to ask a court to drop the extortion case against him today.

Lawyers for Halderman tell Access Hollywood that they're challenging whether or not the evidence is sufficient and will ask the judge to dismiss the case.

Halderman has pleaded not guilty to first-degree grand larceny. He could face up to 15 years in prison if convicted.