Cynthia Collette Vandry appeals the district court’s 1 denial of her Rule 35(b) motion to reduce her sentence. Assuming excusable neglect exists to pardon the untimeliness of her notice of appeal, we affirm the district court’s denial of Vandry’s motion. “There is no provision in Rule 35(b) of the Federal Rules of Criminal Procedure for a motion by a defendant for a reduction based upon a claim of substantial assistance to the [Government.” United States v. Palmer, 297 F.3d 760, 768 (8th Cir. 2002), cert. denied, 537 U.S. 1143, 123 S.Ct. 943, 154 L.Ed.2d 842, cert. denied, 537 U.S. 1213, 123 S.Ct. 1309, 154 L.Ed.2d 1063, and cert. denied, 538 U.S. 937, 123 S.Ct. 1602, 155 L.Ed.2d 340 (2003). To the extent Vandry argues that the Government should have filed a Rule 35(b) motion, she has failed to make a “substantial threshold showing” that the Government’s refusal to file the motion, which was left to the Government’s sole discretion in the plea agreement, was based on an unconstitutional motive, and the Government’s refusal is therefore not subject to judicial review. See United States v. Marks, 244 F.3d 971, 975 (8th Cir. 2001). The district court’s judgment is affirmed. See 8th Cir. R. 47B.