The FCC regulations state the following about repeater and auxiliary station interference:

§ 97.205 Repeater station.
(c) Where the transmissions of a repeater cause harmful interference to
another repeater, the two station licensees are equally and fully respon-
sible for resolving the interference unless the operation of one station is rec-
ommended by a frequency coordinator and the operation of the other station
is not. In that case, the licensee of the non-coordinated repeater has primary
responsibility to resolve the interference.

§ 97.201
(c) Where an auxiliary station causes harmful interference to another auxil-
iary station, the licensees are equally and fully responsible for resolving the
interference unless one station’s operation is recommended by a frequency
coordinator and the other station’s is not. In that case, the licensee of the
non-coordinated auxiliary station has primary responsibilty to resolve the interference.

§ 97.3 Definitions.
(a) The definitions of terms …
(22) Frequency coordinator. An entity, recognized in a local or regional area by amateur operators whose stations are eligible to be auxiliary or repeater stations, that recommends transmit/receive channels and associated operating and technical parameters for such stations in order to avoid or minimize potential interference.