Amgen is suing Coherus Biosciences over its processes for manufacturing a biosimilar of Neulasta, saying it infringes patented methods for purifying proteins.

Neulasta (pegfilgrastim) brought in $4.6 billion for Amgen in 2016, making up 21 percent of the company’s global sales, with $3.9 billion in the U.S. alone. Neulasta was first approved by the FDA in 2002, for lowering the rate of infections following chemotherapy.

Although its product is still under FDA review, Coherus says it anticipates a commercial launch in the latter half of this year — pending the U.S. Supreme Court’s decision on 180-day exclusivity in a separate case brought by Amgen against Sandoz, for its copycat version of a related Amgen product, Neupogen (filgrastim). The Supreme Court is expected to rule by the end of June.

Amgen’s final material patent for Neulasta expired in October 2015, and several companies have been developing biosimilars. However, the patent on the purification process does not expire until September 2024.