The Toronto Sun reported that administrative staff and numerous union directors said they did not know about the devices.
The pinhole video cameras were reportedly installed in the exit signs on the second floor of the association's offices.
Several female staffers filed grievances, citing the "surreptitious placement" of the cameras, the newspaper said. Worries have also surfaced that videos may be able to be viewed through off-site, computerized connections.
TPA President Dave Wilson claimed the cameras had been placed there by a Toronto security company two years ago. Wilson, who said the board has been aware of the cameras all along, said the cameras were installed when the union was dealing with some "difficult situations."