U.S. tech companies could end up paying billions of dollars in new taxes under a plan the European Commission is considering, according to a report by the Financial Times late Wednesday. According to a draft report seen by the FT, a "digital tax" would be be assessed against companies' revenues rather than profits. The tax, which the FT said was likely to be set at 3%, would apply to tech companies with more than 100,000 users in Europe, and cover everything from ad revenue from Alphabet Inc.'s GOOGL, -1.44% Google and Facebook Inc. FB, -1.73% to subscription fees for companies such as Apple Inc. AAPL, +3.03% and Spotify AB. The tax, which may be announced next week in Brussels, is estimated to raise about 5 billion euros a year, the FT reported. The tax is likely to face stiff opposition from U.S. tech groups, but a number of EU member states, such as the U.K., France and Germany, complain tech companies don't pay their fair share in EU taxes.