This work addresses security risks in a gigabit passive optical network. The completely passive infrastructure enables active monitoring of the distribution network in parallel with data communication. The specification of the gigabit passive optical network allows an occurrence of a risk called a modified end unit. Such a unit does not respect allocated time slots, and as a result, all communication becomes disrupted in both downstream and upstream directions. Generally, the problem can be specified as an attack on a specific port of the control unit. In this work, the modified unit is replaced by a laser with a wavelength of 1310 nm and tested at different power levels in the direction of degrading the port's operational capabilities.