At the same time, if you're rebranding another company's work as your entire business model, what can you expect? That they won't continue to sell their services and products to the rest of the industry they serve, because it would be nice for you to have no competition? Not happening, it's on the company doing the rebranding to come up with compelling exclusive offerings or offerings that just beat out the competition on price or some other metric. You can't expect a foreign manufacturer to just hamstring itself to give you preferential treatment vs similar customers, and even being the first to introduce that manufacturer's goods under your own branding doesn't buy exclusive distributor rights.
If they want to stand out in that kind of market, they need to do the thing and positively differentiate themselves. Their existing reputation is decent and they seem to do well, but realistically what would they sue over, seeing as they're just rebranding imported goods in the first place?