labor work This does not exist in a meaningful manner as an adjective+noun combination.
(i) manual work This is any work undertaken mainly with the hands, usually to create or improve something
(ii) manual labour This is any work undertaken mainly with the hands, but usually involves hard work, e.g. digging, lifting heavy objects, using heavy tools.
Note that the real question is about work and labour. Work is all work, labour is harder, physical work, although it is also used figuratively.
Have a look in a dictionary for the verbs to work and to labour.
"Labor" was and is the Latin word for the same activity that is described by the Germanic word in English, "work" (the word in German is spelled the same except for the vowel). The "u" in "labour" was inserted by the French, adopted by the English, and then removed by the American spelling reformer and lexicologist Noah Webster.
Although there is sometimes a subtle difference in English between a word derived from Latin directly or through French vs. a different Germanic word for the same object or concept, I'm not sure that that is the case with "labo(u)r" and "work."
In English we can say of a physically demanding task, "That's hard work" and we sentence convicts to "hard labor." We speak of "labor camps" and "work camps." Perhaps the lawyers use "labor" instead of work because they wrote in Latin and French long after the rest of the population of England had re-adopted (or continued) English. But I think it would be risky to insist that there is any obvious difference in meaning that would be recognized universally by native speakers of English.