The introduction of what tax sparked the Peasants' Revolt of 1381 in England?

When John Bampton, a royal official, attempted to collect unpaid poll taxes it was a straw that broke the camel's back. Poll taxes had been introduced in England one hundred years earlier to help fund a war. The tax was a percentage fee on any movable thing a person owned. A combination of recovering from a bad spell of the plague and a change from serfdom left tensions high and trying to reinstitute the tax created unrest that quickly spread throughout the country.

https://en.wikipedia.org/wiki/Peasants%27_Revolt