A motion to quash asks the court to invalidate a subpoena — because it's unreasonable, seeks privileged material, was improperly served, or imposes an undue burden on the person or entity it was issued to.
Common grounds for quashing
Failure to allow reasonable time to comply, requiring disclosure of privileged information, and imposing an undue burden without adequate justification are among the most common, court-recognized bases for quashing a subpoena.
Third parties have particularly strong footing
Non-party recipients of a subpoena — someone not actually involved in the lawsuit — often have an easier time arguing burden, since courts are generally more protective of people who aren't parties to the underlying dispute.
Partial quashing is a common outcome
Courts frequently narrow rather than fully quash a subpoena — a motion that proposes a reasonable, narrower scope as an alternative to outright quashing often succeeds even when a full block wouldn't.
Move quickly
Most jurisdictions require a motion to quash to be filed before the compliance deadline in the subpoena — waiting too long can mean losing the objection and being compelled to comply as originally issued.