Get the committee to issue them with a NTC as their must be a bylaw that says you cannot use common property without permission. Also turn off the power at the switchboard to these common rooms so they can nolonger steal your power.
If it is common property you have just as much right to access it as the Pizza owner so go poke around in their when he is their and them ask him to provided a copy of his retntal agreement for the common property or exclusive use bylaw.