(Reuters) - Workplace communication platform Slack Technologies Inc forecast a soft revenue outlook for the first quarter on Thursday, sending its shares down more than 20% aftermarket, on a day major U.S. stock indexes went into a tailspin amid coronavirus fears.

The Slack Technologies Inc. logo is seen on a banner outside the New York Stock Exchange (NYSE) during thew company's IPO in New York, U.S. June 20, 2019. REUTERS/Brendan McDermid

The company warned the coronavirus outbreak could hurt demand for its products as companies might cut back on technology spending and also forecast billings for fiscal 2021 well below analysts’ estimates.

“Forward guidance is a little lighter than you’d expect out of a high-multiple name,” said Rishi Jaluria from research firm DA Davidson and Co.

For the first quarter, Slack expects revenue of $185 million to $188 million, lower than analysts’ average estimate of $188.4 million, according to IBES data from Refinitiv.

The company said it expects billings of $970 million to $1 billion for fiscal 2021, lower than analysts’ average estimate of $1.02 billion.

Slack, which has been called an “email killer”, competes directly with Microsoft Corp’s workplace messaging platform, Teams, which surpassed 20 million daily active users in November last year.

Slack said it had over 110,000 paid users at the end of the fourth quarter, up 25% from last year. As a result, revenue rose 49% to $181.9 million, beating analysts’ estimate of $174.1 million.

However, growth slowed from a 60% surge in revenue the company achieved in the prior quarter.

The growth numbers “might be light of what people expected,” Jaluria said.

The company’s total operating expenses in the quarter leaped 67% to $248.7 million.

Excluding items, the company posted a loss of 4 cents per share, beating analysts’ average estimate of a loss of 5 cents per share.

The stock’s slump comes on a day Wall Street tanked, slamming the book on the longest-ever U.S. bull market amid fears of the coronavirus. [.N]