Although BREIN has no legal power, they can (just like every other person) threaten to sue the site admins.
Till today, no BitTorrent site admin has been taken to court in the Netherlands. However, BREIN does send letters to the owners of the “infringing” sites, or their ISP’s, stating that they could face up to four years in prison or a $54,000 fine. These intimidating letters have proven to be an effective strategy to scare P2P hobbyists away. It’s an easy way out. Sending a letter with a claim doesn’t involve having to actually put forth proof that someone is actually engaging in illegal behavior.
This is how it works from thereon: BREIN promises to drop the case if the site owners, take down their site, publicly admit that they infringed on copyright, promise to never do it again, and (if possible) hand over all available information on their members.
Another tactic BREIN has used is identifying the domain holder of a site, running a background check, and visiting the person at his/her home address. This has become one of the most effective ways in which BREIN puts pressure on its “victims.” We reported on this when it actually happened with the 20 year old operator of TorrentIt (previously 123torrents). After that visit, TorrentIt completely stopped serving torrents.