The workplace communications service company is executing a direct public offering, which bypasses the typical underwriting process.
The reference price is not an offering price, according to an NYSE statement.
Slack's opening price will be determined by the stock's designated market maker based on buy and sell orders collected by the exchange from broker dealers.
Some observers are skeptical Slack will see the kind of share-price pop other new listings have seen this year. Growth at the company is heavily dependent on converting free users to paid users. In addition the company faces increasing competition from Microsoft (MSFT) - Get Microsoft Corporation (MSFT) Report .