When international applications are filed, they are forwarded by the Receiving Office (RO) to the International Search Authority (ISA) selected by applicant.
On occasion, specific ISA's have limited their competencies for specific applications. For instance, the EPO will not act as an ISA for applications with one or more claims directed to a business method. Likewise, the Australian Patent Office has declared that it is not competent for applications with one or more claims drawn to subject matter set forth in "Annex A" (link) of the arrangement between IP Australia and the USPTO.
Nonetheless, quite a few applicants have been filing in these jurisdictions on subject matter that runs afoul of the competencies set forth above. Accordingly, the USPTO issued a notice, telling such applicants to cut it out:
The USPTO has noticed a significant number of international applications filed in the United States Receiving Office (RO/US) under the Patent Cooperation Treaty (PCT) where the applicant has chosen an International Searching Authority (ISA) which is not competent for the subject matter of the claimed invention. This can result in significant delays in the issuance of the International Search Report and Written Opinion of the International Searching Authority . . . To avoid significant processing delays, applicants filing international applications naming either the EPO or IP Australia as the ISA should take care to ensure that the application does not contain any claims for which the selected ISA is not competent.Read the notice here (link)