In the US (and you're looking at an FAA manual, so that implies US rules), this is covered in JO 7110.65, the FAA order covering air traffic control procedures. Flip to page 135 of that PDF (note that the linked version is not yet the currently effective version) for Section 3-7-5:
3−7−5. PRECISION APPROACH CRITICALAREA a.ILS critical area
dimensions are described in FAA Order 6750.16, Siting Criteria
for Instrument Landing Systems. Aircraft and vehicle access to the
ILS critical area must be controlled to ensure the integrity
of ILS course signals whenever the official weather observation is a
ceiling of less than 800 feet or visibility less than 2 miles.
Do not authorize vehicles/aircraft to operate in or over the
critical area, except as specified in subpara a1, whenever an
arriving aircraft is inside the ILS outer marker (OM)or the fix used
in lieu of the OM unless the arriving aircraft has reported the runway
in sight or is circling to land on another runway.
PHRASEOLOGY−HOLD SHORT OF (runway) ILS CRITICAL AREA
It goes on from there to describe further details, including instructions on when to keep the critical area clear and instructions to warn aircraft conducting autoland approaches if the critical area will not be protected.
In short, pilots hold short of the critical area if they're instructed to do so, and controllers tell pilots to do that by simply saying "HOLD SHORT OF (runway) ILS CRITICAL AREA."