Ikeski Deckard, federal prisoner No. 08146-078, appeals the district court’s denial of his motion for reduction of sentence based on substantial assistance, purportedly filed pursuant to Fed.R.Crim.P. 35(b).

A motion for reduction of a defendant’s sentence pursuant to Rule 35(b) must be filed by the Government. United States v. Early, 27 F.3d 140, 141 (5th Cir. 1994). The Government’s refusal to move for a reduction of sentence is unreviewable by the district court absent a “substantial threshold showing” that the decision is based on an unconstitutional motive. Wade v. United States, 504 U.S. 181, 185- *226 86, 112 S.Ct. 1840, 118 L.Ed.2d 524 (1992) (reviewing Government’s refusal to file a motion pursuant to U.S.S.G. § 2K1.1). Deckard does not allege that the Government’s decision not to file a Rule 35(b) motion in his case was based on an unconstitutional motive. Deckard’s Rule 35(b) motion was thus “an unauthorized motion which the district court was without jurisdiction to entertain.” Early, 27 F.3d at 142.

The judgment of the district court is AFFIRMED.