Salesforce and Zendesk, which sell customer relationship management software, expressed concern about Facebook’s $1 billion acquisition of a smaller CRM firm to Federal Trade Commission lawyers reviewing the deal, according to people with direct knowledge of the matter. That’s one reason the proposed acquisition, which just a few years ago would have been waved through, is now in its seventh month of a U.S. antitrust review.

Millions of businesses and brands use Facebook’s messaging apps to communicate with their customers. Salesforce, Zendesk and others were concerned that Facebook could cut off their access to its messaging apps for their businesses as a way of giving Kustomer an advantage in the market, these people said. Facebook has said it wouldn’t do that.