I think the original call was "generalise the strike" calling for people to do more than just go on picket lines, and for anyone else who can (eg: students, unemployed, precarious workers, those who can pull a sickie) to join in with direct action, occupations etc..
rather than a call for a general strike..
twasn't the unions that did the callout in the op either, it was a group of anarchists from the names I recognise on the admin list for the event - Phil Dickens, some SolFeds and IWW's .. noticed Mark Bergfield there as well so guess trots as well.. radical lefties anyway..