Slack, the widely used business communication tool, experienced slowdowns in service Monday as many U.S. employees returned to work after the holidays.

The company called the service problem an “incident” in a statement on its website.

“Customers may have trouble loading channels or connecting to Slack at this time,” the statement said. “Our team is investigating and we will follow up with more information as soon as we have it. We apologize for any disruption caused.”

The website Downdetector, which tracks internet disruptions, recorded a spike in reported problems with Slack at about 10 a.m. Eastern time, and the company posted its statement about the problem at 10:14 a.m. Problems included loading channels and sending messages on the service.

Slack has grown in recent years as an essential workplace tool, with more than 10 million users, many of them in media organizations and companies that have shifted to working from home because of the coronavirus pandemic. More than 750,000 companies use the service, according to the company.