Every patent prosecutor knows, or should know, that restriction requirements are petitionable, but not appealable to the PTAB. However, there is at least one exception to this general rule, and the USPTO’s updated MPEP calls it out with a new section. Specifically, with regard to Markush claims, the Examiner is not allowed to placed a restriction on a single Markush claim following the Haas and Weber cases. MPEP 706.03(y), titled “Improper Markush Grouping” sets forth the following in subsection (III):
III. REJECTION BASED ON IMPROPER MARKUSH GROUPING
When an examiner determines that the members of a Markush group lack either a single structural similarity or a common use, or if the single structural similarity is a substantial structural feature of a chemical compound that is not essential to the common use, then a rejection on the basis that the claim contains an "improper Markush grouping" is appropriate (see subsection II). Note that this is a rejection on the merits and may be appealed to the Patent Trial and Appeal Board in accordance with 35 U.S.C. 134 and 37 CFR 41.31(a)(1). Use Form Paragraph 8.40 to reject a claim on the basis that it includes an improper Markush grouping.
It is interesting that the MPEP fails to cite either Haas or Weber. These cases made clear that a restriction placed on a single claim was, in effect, a rejection that gave rise to grounds for appeal to the Board. In drafting this new section of the MPEP without citing the cases giving rise to the relevant law in the first place, there is the potential that the underlying basis is lost. While it is true that Haas was about a rejection for an improper Markush claim, the underlying issue was more general - “whether or not a single claim which includes a plurality of independent and distinct inventions is legally rejectable.”
You can read for yourself why Judge Markey answered the question in the negative, along with the companion Weber case confirming that §121 does not provide a basis for rejection of a claim. But the point is that the MPEP zeroes in on the more narrow issue of improper Markush claims, whereas there is case law support for the broader notion that if the examiner restricts a single claim, the action is appealable to the Board. This makes sense because it is not like the applicant can simply file a divisional with that claim - doing so will only result in the same restriction (rejection). Because the applicant is provided the statutory right to draft a claim as they see fit, do not let an examiner force an amendment by improperly restricting a single claim.