Stelara is J&J's top-selling drug, accounting for $9.1 billion of the company's $52 billion in global drug sales last year. Sales for the first nine months of this year were $7.3 billion, up 7.9% over the same period last year.

The drug is also approved to treat Crohn's disease, the skin condition psoriasis and a related form of arthritis. It is a biologic drug, meaning it is made inside living cells.

A 2009 law allows companies to make so-called biosimilar versions of biologic drugs that can be substituted for them, much like generic versions of conventional drugs. However, J&J alleges that Amgen failed to follow the legal process required by that law for the companies to litigate any patent disputes.

If Amgen launches its drug, J&J said it would infringe J&J's patent on the drug's active ingredient and on its use for treating ulcerative colitis.

Amgen did not immediately respond to a request for comment.

(Reporting by Brendan Pierson in New York; Editing by Lisa Shumaker)

By Brendan Pierson