If you use the 2003 IBC as your building code, then Chapter 16 is the place to go.

Whether or not support wires are actually required depends upon three factors. One is obviously the seismic area the building is in. Another is the importance factor of the building (hospitals are more important than a storage shed). Look to Table 1604.5 in the IBC.
Lastly is the site class of the soils the building is built upon. Look to Table 1615.1.1 for this.

Once it is determined that your building needs seismic bracing, then an engineered design would need to be made. A commonly used referenced standard for this is a book entitled "ASCE 7".

Under this design (and many others) it is determined that an acceptable method of seismic bracing is to attach 2 #12 iron wires of the same sort used by the ceiling installer to diagonal corners of the troffer in rooms larger than a minimum size of 144 square feet. Smaller rooms do not generally require any bracing.

Because of the complexity of these calculation to merely determine where and when seismic bracing is required, many electricians and inspectors simply require all troffers in commercial buildings to have the diagonal bracing.

Earl