The deal is expected to be half cash and half stock, CNBC reported, and will price Slack at a premium to its current price.
Salesforce is scheduled to release its quarterly earnings report on Tuesday afternoon.
Any deal would value Slack above its current market capitalization, The Wall Street Journal reported. It would represent Salesforce's largest acquisition to date.
Jim Cramer weighs in on the acquisition and what it means for Slack.
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