I ran into this problem at one airport which attempted to prohibit non-fbo fuel being brought onto the airport. This was contested and the airport lost. Please see FAA AC 150/5190-6 Exclusive Rights at Federally Obligated Airports Paragraph 4:" It is FAA policy that the sponsor of a federally obligated airport will not grant an exclusive right for the use of the airport to any person providing, or intending to provide, aeronautical services or commodities to the public and will not, either directly or indirectly, grant or permit any person, firm, or corporation, the exclusive right at the airport to conduct aeronautical activities. The exclusive rights prohibition applies to both commercial entities engaging in providing aeronautical services and individual aeronautical users of the airport. The intent of the prohibition on exclusive rights is to promote fair competition at federally obligated, public use airports for the benefit of aeronautical users. The exclusive rights prohibition remains in effect as long as the airport is operated as an airport, even if the original period for which an airport sponsor was obligated has expired."