Re: Federation Law of restricting cloaking device
you're looking for the Treaty of Algeron...
The treaty reinforced and redefined the Romulan Neutral Zone, and made clear that any violations of the Zone without adequate notification, by either side, would be considered an act of war. The treaty also expressly prohibited the development or use of cloaking device technology by the Federation. Then-Captain Pressman attempted to circumvent this clause in 2358 with the test of a phasing cloaking device developed covertly at least in some part by Starfleet Intelligence aboard the USS Pegasus.
As far as i know, there's never been an actual reason why the Romulans demanded The Federation not to use cloaking technology... it's just part of Trek history that's never been explained
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