Best to have both.

@@ -16,0 +17 @@
+<gloss>by-laws</gloss>

Generally unhyphenated:
https://context.reverso.net/translation/japanese-english/細則

https://en.wikipedia.org/wiki/By-law
A by-law (bye-law, by(e)law, by(e) law), or as it is most commonly known in the United States bylaws, i

It appears to me that jmdict prefers the unhyphenated version of by-law/bylaws.  wikipedia is hyphenated, but this was even disputed on the talk page, and the article itself acknowledges that "bylaws" is most common in the U.S.

They are both correct, so the alternative is "bylaws, by-laws" everywhere, which would also be fine with me.

There are a couple other entries that will need to be fixed if this seems good(or about 10~15 if showing both forms, which no entry currently does).

@@ -16 +16 @@
-<gloss>by-laws</gloss>
+<gloss>bylaws</gloss>