European Union officials appear to be targeting U.S. multinationals for taxation, Treasury Secretary Jack Lew said Wednesday, speaking the day after the EU announced a $14 billion crackdown on Apple.

The EU's attempt to make sure that multinationals are not shortchanging governments "certainly appears to be highly focused on U.S. firms," Lew said at an appearance at the Brookings Institution in Washington, adding that the latest development "reflects an attempt to reach into the U.S. tax base"

While officials have told him that they also have investigated smaller firms from other countries, "the largest actions do appear to be aimed squarely at our tax base," Lew said.

Lew criticized the decisionmaking that led to the case against Apple and efforts to examine other U.S. firms over the possibility that they cut deals with governments to avoid taxation in European countries.

The EU's line of investigation is one that "undermines the spirit of economic cooperation and that is inconsistent with well-established principles of tax law," Lew said.

Lew's remarks included a warning for Europe that attempts to tap the U.S. tax base could backfire. "It undermines the environment in Europe for international business, because it creates an uncertainty that ultimately will not be good for the European economy," he said.

Lew spoke before he was due to leave for China to appear with President Obama at the G-20 meeting of leaders.