Reading more about it, the company they work for, Flagship, had a contract which was expiring on this Friday. They claim they were locked out of the building this past Friday. It seems they began picketing over Twitter not just failing to bargain, but also not offering to re-hire them during the transition to a new contractor, as required by California law. For that little extra bit of Ebenezer Scrooge this is happening just before Christmas.
It seems a little weird to me that Twitter would give janitors badge access during weekends, but not impossible. If Flagship’s contract prohibited them from striking, then it would not be legal, but if they’re already locked out they can’t do the job, anyway. Twitter waited until sometime on Monday to terminate the contract, according to California Labor Federation.