The FAA says it has seen an increase in the unauthorized entry into reduced vertical separation minimum (RVSM) airspace by operators who are not RVSM qualified.
In the examples mentioned by the FAA, pilots utilized a flight plan suffix indicating that they were authorized for RVSM operations, but stating in the flight plan remarks section that they did not actually hold the proper FAA letter of authorization for flight in RVSM airspace.
According to the FAA warning, the agency is considering filing pilot deviations for future instances where that occurs. Before conducting a flight in RVSM airspace, operators are reminded to verify that they hold a valid RVSM LOA from the FAA.
For information on RVSM requirements: http://www.nbaa.org/member/ops/cns/rvsm