Microsoft has privately told European competition authorities that Slack’s antitrust complaint against the tech giant was motivated essentially by sour grapes.

In a recent confidential filing, Microsoft told the European Commission, which oversees competition regulation, that Slack brought its complaint against Microsoft because the lockdown prompted by the coronavirus pandemic has exposed deficiencies in Slack’s messaging product, according to a person who has seen the complaint. In the filing, which runs about 40 pages, Microsoft said the sudden surge in people working from home this year has made more apparent shortcomings in Slack’s product, including its handling of videoconferencing, while also benefiting Microsoft’s competing Teams software, the person said.