J.P. Morgan downgraded Beyond Meat on Tuesday, after the company's stock surged more than 600% from its initial public offering price of $25 through its high on Monday.

The firm, which was the lead underwriter for the red hot May IPO, downgraded the stock to "neutral" from "overweight" and kept its price target of $120. The alternative meat company reported stronger-than-expected earnings last week — its first report since going public.

The stock is "beyond our price target," J.P. Morgan analyst Ken Goldman said in the note to clients. The share price has already exceeded the price target of every analyst on Wall Street and short sellers have lost more than $400 million betting against the plant-based burger maker's stock since it went public, according to research firm S3 Partners.

"This downgrade is purely a valuation call," Goldman said. "As we wrote last week, 'At some point, the extraordinary revenue and profit potential embedded in BYND… will be priced in' – we think this day has arrived."

Shares of Beyond Meat fell 18% to $136.48 in early trading. While investment banking and analyst research are separate units at major firms, investors likely still found it surprising that the lead underwriter would downgrade one of the companies it took public this early.

The company also announced on Tuesday that this week it will launch a "meatier" version of its plant-based burger.