The 1096 People's Crusade were joined mostly by peasants, led by the priest Peter the Hermit independently of their lords. What was the status of these peasants' trip? Were they free to take trips and not serve their lords, or did this fall under some exception, or did they violate their feudal obligation by going on this trip?
... Pope Urban the Second who presided at the assembly seconded the proposition of Peter the Hermit with so much force and eloquence that the whole council exclaimed unanimously "God wills it; let us depart!!"
and from the same page:
Neither Phillip of France nor the other European monarchs joined the league but permitted their vassals and subjects to follow the general movement.
The above From The Universal Chronologist, and Historical Register, from the ..., Volume 1 By William Henry Ireland, Joseph Martin
So, it appears that these peasants probably had permission from their respective lords, as it was being endorsed by the Pope, and supporting a cause endorsed by the church would have possibly curried favor for these nobles, while refusal could have incurred the churches wrath.