Which of the following is NOT a reason for filing a protest, as defined at FAR 33.101?

Filing a protest is a mechanism allowed under FAR 33.101, designed to address various grievances regarding procurement actions. The appropriate reasons to file a protest typically relate to specific actions taken regarding the solicitation or award that a vendor believes have been unfair or non-compliant with established regulations.

When considering the correct answer, the idea is that a protest must be rooted in actions that directly affect a vendor's participation in a contract competition. An award or proposed award of the contract is a direct action that a vendor can contest, as it directly impacts their opportunity to receive a contract. Similarly, a cancellation of a solicitation affects vendors who are interested in bidding, while allegations of impropriety concerning a contract award pertain to irregularities in the award process.

In contrast, the action of protesting another vendor's protest lacks the basis for formal protest procedures as outlined in FAR. A vendor's concerns about another vendor's actions do not constitute a substantive reason for a protest in the realm of federal acquisition regulations. Therefore, a protest arising simply from the knowledge of another competing vendor's protest is not a validated cause for filing under the existing regulations, making it the correct choice.