from ASLEF's own website:-
"Over 50% of ASLEF members issued with ballot papers voted for industrial action according to Electoral Reform Services who conducted the ballot for the union. Of those who returned them, 1,040 said 'I am prepared to take part in a strike' while only 116 voted 'No'"
that's not 90% support in my book - 90% of those who could be bothered, maybe.