The Wild Oath

When those who are not of Elven descent approach the wilds of Galaed Vala - the forests, to be particular, they are almost always met by Elves - they keep a close eye on the borders of their territory.
To be allowed entry to the forests, a demand is made of the non-elves, that they swear to the Wild Oath. The oath must be made in Elven, and those who do not speak the language are coached in the verses required.

In general, the Oath requires the trespasser to swear they will not bring harm to any inhabitant of the forest beyond what is necessary to survive. This means that they just not kill creatures for sport, must not cut live wood, and so on.
The consequences of breaking the vow are unknown, but they are likely dire.