When citizen activists dare to challenge the Establishment, the Establishment often reacts with threats and intimidation. This is true whether the Establishment is the local planning board, the school board, a political party, or the neighborhood homeowners' association. Intimitation doesn't have to be as overt as a group of policemen threatening to arrest you. It can be subtle threats against you, your family, or your job.
If you or your organization fins yourself in this situation, the Western Organization of Resource Councils (WORC) has a three-page guide for you. WORC is pretty progressive and you may not like all of their policy agenda but their advice for standing up to intimidation is solid.