Denied boarding and cancellation are covered by Article 17 of Regulation [EC]261/2004
The regulation applies to all flights operating from an EU airport and to flights operating to EU airports from outside the EU when operated by an EU airline.
This applies to all flights including charters.
There are however getout clauses for the airlines, known as extraordinary circumstances.
Recital 14 cites five potential examples of extraordinary circumstances, they are
Political instability
Meteorological conditions incompatible with the operation of the flight
security
unexpected flight safety shortcomings
strikes
Most airlines are pretty quick at hiding behind one of these.
Hen Ddraig
Time to spare, go by air