I've added a few links, over there on the right margin, to the band plans for the 2m and 70cm amateur bands. The band plans are "gentlemen's agreements" amongst us all that divide the band in to different areas for different uses.
The band plans also incorporate FCC regulations, namely our frequency allocations.
Do they have the force of law? In some cases directly, yes. For example you may not, as a matter of FCC rule, operate anything but CW between 144.000 and 144.100.
In other cases, indirectly, yes. The FCC has said that it is good amateur practice to follow the various band plans and since §97.101(a) of the amateur service rules says "In all respects not specifically covered by FCC Rules each amateur station must be operated in accordance with good engineering and good amateur practice.", then it follows that band plans have the force of law!
For an excellent discussion of band plans, please see this discussion from the Utah VHF Society.