The legislation was stalled over a fight on an Internet tax ban.
Defense hawks are calling for extra funding.
Sanders had expressed concern about North Korea during last week's debate.
Sen. Chris Coons (D-Del.) said he will try to bolster funding in the appropriations process.
The legislation would require the Obama administration to crackdown on the isolated country.
The letter come as the Senate is expected to back new sanctions.
Reid calls the decision "short-sighted" and a "stunning move."
The two senators have spent the past week in New Hampshire.
Vicki Needham 02/09/16 07:14 PM EST
The Senate is expected on Thursday to send a customs enforcement conference report to President...
His comments come as Republicans battle in New Hampshire.