The Occupiers proclaimed that the Hammonds inspired their initial protest, and their release from prison was cited as demand of the group occupying the Malheur National Wildlife Reserve.
OPB's article "Why Were The Hammonds Sent Back To Prison" explains the situation:
The Hammonds, father and son ranchers from the area, were convicted for setting a fire in 2001 that burned on federally-maintained land. The son, Steven, was convicted for setting another fire in 2006, which he said was a backburn to prevent wildfire from spreading to his property.
The Hammonds received prison sentences of roughly a year or less each for their actions, but mandatory minimums came into play because of the Anti-terrorism and Effective Death Penalty Act that Congress passed in 1996.
The following groups have been referenced in news media, either as formally taking action in relationship to the protest in support of the Hammonds or involved in the occupation of the Malheur National Wildlife Refuge.