National ministers Gerry Brownlee and Nikki Kaye have also had their offices attacked, presumably by people opposed to the TPP.
Security on the Parliamentary precinct in Wellington has ramped up in recent months, with more doors with access control and improved CCTV capability.
However, the Parliamentary Service, which provides support services to the House of Representatives and MPs, has concerns about its staff that work in electorate offices.
In a recent presentation to Parliament's government administration committee, it said 54 out of 144 electorate offices did not meet minimum security standards.
The unsafe offices were not identified, and there was no suggestion those that had been attacked were unsafe.
A spokeswoman for Parliamentary Service told the Herald it was working hard to have all offices up to standard by September.
MPs are given a capped allowance to cover the cost of renting and running offices.
Parliamentary Service had paid for all of the upgraded security measures to comply with minimum standards. Some requirements include an enclosed reception area, a safe retreat area for employers and visitors, and a duress system.
Work and Income is this year trialling new layouts at two of its offices in a bid to bolster security in the wake of the 2014 Ashburton shootings. Winz has done away with its traditional open-floor plan at its Wellington and Levin offices. It has instead used screens to partition areas.
The double-murder trial of Russell John Tully, 49, started at the High Court in Christchurch yesterday.
He denies two charges of murdering Winz employees Peggy Turuhira Noble, 67, and Susan Leigh Cleveland, 55,and attempting to murder Lindy Louise Curtis and Kim Elizabeth Adams.
