Yes, an accused service member, through their defense counsel, can challenge the legal sufficiency of the charges before their arraignment at a court-martial. This is typically done by filing a motion to dismiss with the military judge. The arraignment is the formal reading of the charges in court, where the accused enters a plea. A challenge to the charges themselves is a pretrial matter that should be resolved before the accused is required to plead.
The motion to dismiss would argue that the charge sheet is legally deficient. There are several grounds for such a motion. The attorney could argue that the charges fail to state an offense under the UCMJ—meaning that even if the facts alleged are true, they do not constitute a crime. They could also argue that the charges are unconstitutionally vague, making it impossible for the accused to know what they are being accused of and to prepare a defense. Another ground is a lack of jurisdiction.
The military judge will review the motion and the charge sheet. If the judge agrees that the charges are legally insufficient, they have the authority to dismiss them. This can result in some or all of the charges being thrown out before the trial even begins. This pretrial motion is a critical tool for a defense attorney to protect their client from having to face a court-martial on charges that are not properly drafted or legally sound.