Thousand Oaks-based biotech giant Amgen faces a lawsuit seeking to block it from selling a biosimilar of AbbVie’s popular Humira.

The rheumatoid arthritis medicine is Abbvie’s best seller. Sales were up 17 percent in the second quarter to $4.15 billion and accounted for 61 percent of AbbVie’s 2015 revenue.

Abbvie claims Amgen’s proposed copy would infringe at least 10 patents.

Humira includes a complex protein manufactured in living cells rather than by chemical synthesis. Its active ingredient is the antibody adalimumab.

“Amgen seeks to copy AbbVie’s work and ignore AbbVie’s patents,” AbbVie said in the complaint, filed Aug. 4 in federal court.

Amgen said it wouldn’t comment on the litigation, but said its own version, known as ABP 501, is working its way through the U.S. Food and Drug Administration.

In July, an FDA panel voted that it should be approved to treat seven chronic inflammatory conditions.

“The FDA Advisory Committee’s favorable vote last month was an exciting step toward recognizing ABP 501 as an important treatment option for patients with inflammatory diseases,” said Kelley Davenport, a company spokeswoman. “We look forward to continuing to work with the FDA as they complete their review” of the company’s application.

• Bloomberg News contributed to this report.