The two that I've heard are money and politics.

RFC 2321 suggests that they are "political and religious" layers. https://www.rfc-editor.org/info/rfc2321/

   In this document we introduce a new hardware-based tool for diagnosis
   and repair of network related hardware and software problems. This
   tool is best suited to addressing nondeterministic problems such as
   those described above. This tool has broad areas of application at
   all levels of the OSI model; in addition to uses in the physical,
   network, transport and application layers, it has been used to
   successfully address problems at the political and religious layers
   as well.