Lexmark International, Inc. v. Static Control Components, Inc.
Ink cartridges and toner are often very expensive (in fact, printer in is the 7th most expensive liquid in the world), and third party workarounds such as the one in this case are an attempt to lower prices for the consumer. Alternately, there's LaserMonks, a group of Cistercian monks who sell cartridges individually and at volume for much lower prices than retail, and whose proceeds go to sustain the monks and fund charitable works. The European Union has also passed a law that forbids printer manufacturers from installing chips in their cartridges that prevent consumers from refilling the ink instead of buying a new cartridge. The law went into effect in 2006.
After this ruling, Lexmark added patent infringement theories to its case, which was finally concluded in 2014 with a loss for Lexmark.