As reported last week, the mass meeting was arranged in protest against compulsory redundancies.
Tony Benn, NUJ Member of Honour and former Labour cabinet minister, spoke to staff in the canteen of the London-based company at three o'clock.
FT management has asked for 20 volunteers for redundancy, but only 11 have come forward, the NUJ release said.
"There's a real sense that there's no need for these redundancies. Everybody feels angry about this," the acting father of chapel at the FT, David Crouch, told Journalism.co.uk.
"The company's doing exceptionally well and it's been very hard for the staff here."
The manner in which staff had been identified for redundancy was a primary concern, he added.
"The idea is to show concern and stand up for journalism," NUJ campaigns officer, Miles Barter, told Journalism.co.uk.
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