In October 2014, Slack raised $120m in venture capital with a $1.2bn valuation.
Slack Technologies is reportedly in funding negotiations with investors, with a potential $2bn valuation on the cards.
Citing people familiar the matter, Bloomberg reported that the funding round has not yet closed, and the size and terms of the agreement may change.
In October 2014, Slack raised $120m in venture capital with a $1.2bn valuation led by Kleiner Perkins Caufield & Byers and Google Ventures.
Slack, which develops software for workplace collaboration, signed up 8000 customers within 24 hours of its launch in August 2013. The company had over 500,000 active daily users in February this year.
The company originally raised about $43m in April 2014.
Slack is a team communication tool founded by Stewart Butterfield. It started as an internal tool used by his company Tiny Speck in the development of Glitch online game.
In 2012, Butterfield and the founders decided to shut down Tiny Speck and return $5m cash it had to stakeholders.
However, other investors suggested the founders keep the money and open a new business, which then became Slack.
Slack has also raised financing from Accel Partners, Andreessen Horowitz and and The Social+Capital Partnership.
Butterfield said Slack was planning to double its head count this year from 63 in 2014.