LONDON — The European Commission is said to be planning to charge Google with using its dominant position in online search to favor the company’s own services over others, in what would be one of the biggest antitrust cases here since regulators went after Microsoft.

Europe’s competition chief, Margrethe Vestager, is expected to make an announcement in Brussels on Wednesday that Google has abused its dominant position, according to two people who spoke Tuesday on the condition of anonymity.

The decision to push ahead with a so-called statement of objections is the latest twist in the lengthy investigation into Google’s activities in Europe, where it holds a roughly 90 percent share in the region’s search market. If Europe is successful in making its case, the American tech giant could face a huge fine and be forced to alter its business practices to give smaller competitors like Yelp greater prominence in its search queries.

A representative for Google declined to comment on any potential action by the European authorities. But in an internal memo to employees, first obtained by the technology news site Re/code, the company said it expected the commission to file a statement of objections about how the company displays search results, particularly for shopping. It also expected the authorities to open an investigation into Android, the Google software that runs a majority of the world’s smartphones.