Shares of the San Francisco workplace collaboration software platform at last check were down nearly 1% at $41.85.
"Customers may experience issues connecting to Slack to loading channels at this time," the company said on Twitter. "Our team is on the case and we will keep you posted. Apologies for any disruption."
The company said customers may have trouble loading channels or connecting to Slack.
At 10:44 EST, the company said on its website that it was still investigating the ongoing connectivity issues with Slack. "There's no additional information to share just yet, but we’ll follow up in 30 minutes. Thanks for bearing with us."
"Back to work traffic jam on Jan 4 in a remote working world," one person commented on Twitter.
Slack also reported problems in early October.
The company has seen increased activity due to the coronavirus pandemic, which has forced many employees to work from home.
On March 10, the company said concurrent users passed 10 million, a figure that jumped to 10.5 million six days later and then 12.5 million on March 26, the Verge reported late last year.
About 750,000 companies use the service.
According to Slack, using the app reduces emails by 32% and meetings by 27% The company says it has more than 10 million daily users.
The acquisition had been widely anticipated after word of talks between the companies first surfaced.
It will combine Slack, a highly visible messaging platform, with Salesforce, which makes productivity tools used by companies to improve sales and services.
"Our teams are aware and are investigating the issue," Slack said in a statement. "We know how important it is for people to stay connected and we are working hard to get everyone running as normal. For the latest updates please keep an eye on @slackstatus and status.slack.com.”