We analyze mergers between strategic data intermediaries collecting consumer information that they sell to firms competing in a product market. We show that a merger: (a) reduces the intensity of competition in the product market through a change in the selling strategies of merging intermediaries; (b) increases data collection, reducing consumer surplus through a better rent extraction. We argue that the role of Big Tech companies acting as strategic data intermediaries in the market for information should be included in antitrust analysis.