But creating a virtual free trade zone for data — if such a thing is possible — raises questions about what happens outside that zone. A spokesman for Mr. Breton, who is on a panel advising the commission’s strategy on cloud computing, said that his statement was “not about protectionism” but about ensuring “customers will receive the proper level of guarantees in terms of data protection and access across Europe.”

It is not entirely clear what creating European clouds would really entail, or how one would draw digital borders. Large American providers of cloud services, like Amazon, have data centers throughout Europe. And even European companies with American subsidiaries are vulnerable to American law enforcement requests, a point of contention between the governments.

American technology companies, as well as the American government, have voiced unease publicly and privately.

In a recent speech, Cameron F. Kerry, the general counsel of the United States Commerce Department, said: “It would be a sad outcome of the surveillance disclosures if they led to an approach to Internet policy-making and governance in which countries became a series of walled gardens with governments holding the keys to locked gates.”

“But that is where we will end up if all data has to stay on servers located in the nation in which a citizen lives or where a device is,” he said. In his view, the regulation might restrict the flow of information among citizens, as is the case in China with barriers that are called the Great Firewall. “The digital world does not need another Great Firewall — in Europe or anywhere else.”

Anna-Verena Naether, policy manager for DigitalEurope, a trade group of international technology companies, including American and European giants like Apple, Microsoft and SAP, said, “We have to make sure it doesn’t lead to a Fortress Europe approach.”

Mark Taylor, a partner at the London office of Hogan Lovells, a law firm that represents a number of businesses that use cloud services, as well as companies that provide it, said, “There’s a risk of going too far and effectively putting a significant element of this in reverse, and in the current economic situation my feeling is you have to be jolly careful about anything that’s going to have a broader economic impact.”