Workers agreed to hold a strike ballot over the allegedly authoritarian regime introduced since Shaun Brady, a Blairite, took over as general secretary.
The GMB union, which represents staff, claimed that Mr Brady, a Labour loyalist who last summer defeated leftwinger Mick Rix, had failed to make the transition from a South West Trains driver to the head of a major organisation.
Paul Kenny, GMB London leader, said: "There is a degree of immaturity in the management approach. You can't just come in and bulldoze your way around."
A caretaker was suspended shortly after Mr Brady took office but was reinstated when it was realised the employee had the keys to the office and officials were locked out.
Other workers have been accused of being pro-Rix while those off work through sickness have complained of visits from senior officials trying to force them back into the office.
"The whole thing has gone pear-shaped. There are allegations of victimisation, bullying and harassment," Mr Kenny said.
A spokesman for Mr Brady said: "We are keen to find a resolution and would urge members to accept our invitation to a meeting at the earliest opportunity."
