I understand what you mean, but I'd really strongly object to the use you've made of the term though as that is precisely the use which was introduced by the right-wing for the purposes of delegitimizing labour organization by conflating labour organization with the anti-competitive nature of cartels in the ideological and rhethorical climate of Neoliberalism that has continuously fetishized supposed competition and playing off our fear of it while nevertheless tending the conditions that promote cartelization of the global economy to the hilt.
The difference is that cartels are firms controlled by capitalists for the purpose of profit and capital accumulation. They fix prices for this purpose. Workers do not, because by their very nature capital accumulation is the logic of the capitalists' material interests, and so in strong contradiction, in the final analysis, with the material interests of labour. Cartel on this definition you've used would then just mean 'price control'. But is then a monopoly or the government a cartel when they respectively fix or regulate prices? The purpose of the introduction of the term was to refer to new formations, concentrations and centralizations of capital in the late 19th century for purposes of overcoming the economic slowdown of this period. It seems harmful, confused and inevitably confusing to widen the meaning of the word so broadly.
I obviously agree that labour should organize, and there are circumstances in which markets might be tolerated in very restricted ways from a socialist perspective, and in such markets labour should therefore of course be organized in such a way as to control production and therefore prices. But the assumption in your question that markets are 'legitimate' in general strikes me as deeply problematic and politically un-Marxist.