Shares of Slack Technologies Inc. /zigman2/quotes/212180539/composite WORK -1.28% are off more than 2% in premarket trading Friday after Goldman Sachs analyst Heather Bellini downgraded the stock to sell from neutral. "While we continue to view Slack as a best-in-class team messaging offering that is favored by the technical community, we expect Microsoft Teams to continue to try and leverage its packaging within Office 365 to drive increased adoption, thus creating the potential for a more competitive environment," she wrote. This competitive landscape could pressure Slack's long-term growth rate and its ability to penetrate its addressable market, in her view. Bellini also sees "elevated risk" of customer churn for Slack given the company's "significant" exposure to small- and medium-sized businesses "as well as exposure to industries directly impacted by the pandemic." She maintained a $30 price target on the stock, which is up 63% over the past three months as the S&P 500 /zigman2/quotes/210599714/realtime SPX -0.44% has risen 29%.