Treasury Secretary Jacob Lew has reportedly fired off a letter to officials in the European Union complaining about recent tax investigations of U.S.-based multinationals like Apple, McDonald’s, Amazon and Starbucks.

The letter was sent Thursday to European Commission President Jean-Claude Juncker and EU antitrust chief Margrethe Vestager, according to Reuters.

“While we recognize that state aid is a longstanding concept, pursuing civil investigations—predominantly against U.S. companies—under this new interpretation creates disturbing international tax policy precedents,” he wrote. “We respectfully urge you to reconsider this approach.”

The European Commission has been probing special tax deals that some U.S.-based multinational companies have set up with some European countries with low tax rates such as Ireland, the Netherlands and Luxembourg (see EU Sets Sights on Forcing Firms to Pay Nations Tax Where Due). Juncker has also threatened to investigate Google’s parent company Alphabet’s arrangement with the United Kingdom (see Google’s Tax Deal with U.K. May Be Next in Line for EU Probe).

Lew's letter was obtained by Accounting Today. In it, Lew acknowledged the United States shares the EC's strong interest in preventing major multinational companies from shifting income from higher-tax countries to low- or no-tax jurisdictions. “President Obama has proposed a robust business tax reform plan that would address this problem, and he repeatedly has urged our Congress to enact it into law as soon as possible,” he wrote. “Moreover, the United States has played a leading role in the G-20 and the OECD Base Erosion and Profit Shifting (BEPS) project. The BEPS project has produced a broad set of measures to prevent and deter international corporate tax avoidance. Countries and companies around the world are responding by reforming their policies and behavior.”

However, Lew said the U.S. is disappointed that the European Commission’s Directorate-General for Competition, or DG COMP, “appears to be pursuing enforcement actions that are inconsistent with, and likely contrary to, the BEPS project.”

“First, DG COMP has sought to impose penalties retroactively based on a new and expansive interpretation of state aid rules,” said Lew. “We appreciate that the state aid doctrine is a longstanding component of EU competition law. We also recognize that the selective application of tax rules could potentially constitute impermissible state aid. Our team is not aware, however, of any previous instance-in the many decades of state aid jurisprudence- in which DG COMP has applied its current theory of selectivity. Instead, DG COMP appears to be adopting an entirely new legal theory and applying it retroactively in a broad and sweeping manner. This raises serious concerns about fundamental fairness and the finality of tax rulings throughout the entire European Union.”

Lew also argued that the Directorate-General appears to be targeting U.S. companies disproportionately. “The legal theory underlying its investigations logically should apply to all multinational firms, not just those based in the United States,” he wrote. “Yet three of the four current transfer pricing cases reportedly involve Member State arrangements with U.S. firms. In addition, public reports suggest that DG COMP is seeking billions of dollars in penalties from U.S. firms-far more than what it is seeking from non-U.S. companies.”

Lew contended that DG COMP's approach appears to target, in at least several of its investigations, income that EU member states have no right to tax under well-established international tax standards. “U.S. multinationals generally do not conduct the cutting-edge research and development that creates substantial value in the European Union, and as a result, comparatively little of their income is attributable to their European operations,” he said. “We recognize that the U.S. system will only tax this income upon repatriation, and many U.S. firms are choosing to defer paying tax liabilities by keeping income overseas in low-tax jurisdictions. This is a serious problem that we seek to address through President Obama's business tax reform plan and the BEPS project. This problem, however, does not give Member States the legal right to tax this income. Doing so would directly harm U.S. taxpayers. When U.S. companies repatriate revenue- as tax reform proposals from both U.S. political parties would require them to do within a fixed timeframe any assessments paid to Member States could be eligible for foreign tax credits. This loss of revenue would impose a direct cost on American taxpayers.

Lew said the Directorate-General’s approach could undermine U.S. tax treaties with EU member states. “As you know, Member States have exclusive authority over income tax under EU law,” he pointed out. Accordingly, the United States does not have an income tax treaty with the European Union. DG COMP's new assertion of authority raises serious questions about this relationship and the finality of income taxation-related dealings with Member States. We expect that this new uncertainty could damage the business climate in Europe and deter foreign direct investment.”

Last month, Robert Stack, the U.S. Treasury’s deputy assistant secretary for international tax affairs, met with EU officials and relayed his concerns about the probes.

“While in the Starbucks case, the sums were relatively modest, 20 million to 30 million euros, they may be substantially larger, perhaps in the billions in other cases,” Stack told Bloomberg News. “The retroactive application of these new approaches calls into question the basic fairness of these proceedings.”

Lawmakers in the U.S. have also begun sounding the alarm about the probes. Last month, a group of senators from the Senate Finance Committee wrote to Lew warning the European Union’s state aid investigations could lead to retroactive taxation on multinational enterprises and have an adverse impact on U.S.-based companies. They included Senate Finance Committee Chairman Orrin Hatch, R-Utah, ranking member Ron Wyden, D-Ore., and committee members Rob Portman, R-Ohio, and Chuck Schumer, D-N.Y.

“Our concerns are driven not only by these initial cases, but also by the precedent they will set that could pave the way for the EU to tax the historical earnings of many more U.S. companies—in some cases, the earnings in question could have been generated up to a decade ago,” they wrote. “We urge Treasury to intensify its efforts to caution the EU Commission not to reach retroactive results that are inconsistent with internationally accepted standards and that the United States views such results as a direct threat to its interests. We also ask that you consider, under section 891, whether U.S. corporations are being subjected to discriminatory taxation.”