Slack is working on integrating Microsoft Teams calling features into its chat app. The integration would allow users of both rival services to call each other, bridging an important gap between the communications apps. “We’re working on Teams integrations for calling feature,” said Slack CEO Stewart Butterfield on an analyst call, reports CNBC.

Slack hasn’t revealed exactly how the calling integration will work, but the company previously made its apps easier to use with Microsoft’s Office 365 apps last year. This included Outlook calendar and mail integration into Slack along with access to OneDrive documents. Slack created these apps using Microsoft’s publicly available APIs and without any close collaboration between both companies.

It’s not clear when this new Slack and Microsoft Teams integration will be available or whether the two companies are partnering to enable calling between the communications services. It would be surprising to see the two firms working together, given the intense competition.

Microsoft has been racing to beat Slack to key business customers, and it passed Slack daily active users last year. Both services have seen big increases in demand following the novel coronavirus pandemic. Microsoft Teams usage soared to 44 million daily active users earlier this month, and Slack revealed this week that it hit a new record of 12.5 million concurrent users.