Ken Cornell Roberson appeals the denial of his motion for a reduction of his sentence pursuant to 18 U.S.C. § 3582(c). The district court denied the motion, determining that it lacked authority to reduce Roberson’s sentence below the statutory minimum term of imprisonment. The Government has moved to dismiss the appeal as frivolous. See 5th Cm. R. 42.2. Roberson argues that he was entitled to a motion for a downward departure pursuant to 18 U.S.C. § 3553(e) and that the Government declined to file such a motion because of improper motives.

*531 Section 3582(c) provides a mechanism by which a defendant may seek the “retroactive application of a subsequently lowered guideline range.” See United States v. Shaw, 30 F.3d 26, 29 (5th Cir. 1994). It does not authorize a sentence below the statutory minimum term of imprisonment. If a defendant provides assistance to the Government, the Government may, but is not required to, file a § 3553(e) motion permitting a district court to depart below the statutory minimum term of imprisonment. Wade v. United States, 504 U.S. 181, 185, 112 S.Ct. 1840, 118 L.Ed.2d 524 (1992). Although a district court will review the Government’s decision not to file such a motion if it was based on unconstitutional motives, Roberson’s vague allegations of an improper motive are insufficient to make the substantial threshold showing required. See id. at 186, 112 S.Ct. 1840.

Without a motion to depart pursuant to § 3553(e), the district court had no authority to sentence Roberson below the statutory minimum, as it correctly determined and, therefore, did not abuse its discretion in denying Roberson’s § 3582(c) motion. See Shaw, 30 F.3d at 28. For these reasons, the Government’s motion to dismiss is GRANTED, Roberson’s motion for appointment of counsel is DENIED, and this appeal is DISMISSED. See 5th Cir. R. 42.2.