This trend of Costco hard-lining brands for better prices is actually pretty common, with the store even going so far as to pull Apple products in 2010, according to HuffPost. Luckily, the brands have since made amends and Costco has resumed stocking their products (via Costco).

However, these hard stances on price negotiations aren't just for brands that compete with Kirkland. In fact, according to The New York Times, once Starbucks failed to pass along savings when coffee beans dropped in price, and as a result Costco chief executive Jim Sinegal warned his friend and Starbucks chairman, Howard Schultz, that he would remove Starbucks products from Costco stores unless they cut prices accordingly. Starbucks relented, but not without Schultz asking Sinegal: "Who do you think you are? The price police?" Sinegal responded emphatically that he was just that. As a result, you can still find Starbucks products at Costco stores and online (via Costco). 

Now, it seems, the Kirkland brand has taken over much of that "price policing," simply by offering fair prices for comparable products that pressure name-brand competitors like Poland Springs and even Gillette to drop their prices just to compete (via CNN).