A preliminary investigation by Mr. Almunia’s office found that the Johnson & Johnson unit in the Netherlands, Janssen-Cilag, made the payments to stop Novartis from selling generic fentanyl skin patches in the Netherlands for more than a year, from July 2005 until December 2006. That kept prices artificially high, according to the European Commission, the European Union’s administrative body that enforces antitrust law. Mr. Almunia’s office would not disclose the amount of money that Janssen-Cilag paid to Sandoz, nor would officials indicate whether the investigation would go beyond the Netherlands.

Both companies will have the chance to formally respond to the accusation.

A spokesman for the Johnson & Johnson subsidiary said in a statement that the company had acted properly. “Janssen continues to believe that these arrangements were legitimate,” the spokesman, Stefan Gijssels, said on Thursday. “Janssen supports a sustainable health care system, where patients have access to both innovative and generic drugs,” he said.

Sandoz said in a statement that it and Novartis “operate to the highest of standards and take the position of the commission seriously.” It also indicated that it and Novartis would seek to rebut the accusations made by the commission by using their “rights of defense as provided for in the process.”

The case is the latest in a series of actions by authorities in Europe and the United States to crack down on so-called pay-to-delay tactics by pharmaceutical companies and comes at a time when the biggest name-brand drug makers are losing billions of dollars in sales to generic competition as best-selling drugs lose their patent protection.

United States regulators have argued for years that such arrangements were anticompetitive. But the pharmaceutical companies have argued that the deals in question were simply legal settlements over patent disputes that helped the companies avoid costly litigation.

The deals typically unfold as part of the peculiar requirements of the federal law governing generic-drug approval, known as the Hatch-Waxman Act. Under that law, generic companies typically seek approval to make a copycat drug before the patent expires because the first company to challenge the patent’s validity wins the right to exclusively sell its version for 180 days. The brand-name company often then challenges the generic company’s right to make the drug, contending the patent is valid.