I think this derives from a standard widely used in the computer business, RFC 2119 (see ref), which says (inter alia):

. . . several words are used to signify the requirements in the specification. These words are often capitalized.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
RFC 2119.

1. MUST This word, or the terms "REQUIRED" or "SHALL", mean that the
definition is an absolute requirement of the specification.

2. MUST NOT This phrase, or the phrase "SHALL NOT", mean that the
definition is an absolute prohibition of the specification.

3. SHOULD This word, or the adjective "RECOMMENDED", mean that there
may exist valid reasons in particular circumstances to ignore a
particular item, but the full implications must be understood and
carefully weighed before choosing a different course.

Although your anbud may have nothing to do with computer procurement, these standard phrases are often used for all kinds of procurement bids because they are defined and well understood. For that reason, I think I would use them (and with SHALL, SHOULD in capitals). See numeerous Google refs to "SHALL requirement"