Renwick McLean contributed reporting from Madrid for this article.

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European Union regulators switched their attention Monday to Spain from France as a battle to knock down barriers to trade within the 25-member bloc looked set to intensify.

In an echo of action taken against France last week, EU officials gave the Spanish government two weeks to say whether they modified energy regulations last month in order to block cross-border deals, including a proposed takeover of the Spanish utility Endesa by E.ON of Germany.

A government decision to give the Spanish energy regulator enhanced powers to approve such deals "has given the commission cause for concern," said an EU spokesman, Oliver Drewes. "In our view, the new national provisions could create obstacles" to international takeovers, Drewes said.

As part of a series of bold actions aimed at preventing a rash of copy-cat protectionist moves spreading across the region, EU officials also are planning to bring a lawsuit against the Polish government for blocking a banking deal.

In that case, the EU's internal markets commissioner, Charlie McCreevy, will formally recommend that the European Commission sue Warsaw for unfairly applying the terms used to privatize a Polish bank to stymie expansion of the Italian bank UniCredit into the country's financial services market.

In addition, McCreevy and the EU's competition commissioner, Neelie Kroes, are expected as soon as Tuesday to warn European stock markets to take steps to separate share-trading from services that take place after trading, known as clearing and settlement. Without greater competition in this area of financial services, say EU officials, the cost of trading and raising capital on stock markets in Europe will remain too high. But even as the EU bares its teeth, questions are likely to remain over its bite. Even when member states do break European laws on free trade, regulators are forced to take their government to the European Court of Justice in a cumbersome process that can take years.

An even greater challenge for EU officials is dissuading countries from crafting policies that break the spirit of the European single market but that do not infringe the letter of the law.

"Law is of limited use in the immediate future," said Chris Bright, a regulatory expert based in London and a consultant to the law firm Shearman & Sterling. "A key issue is whether diplomacy will prevail, because without that there is a threat to the whole European project."

Last week, the EU put Paris under pressure to explain events leading up to a proposed merger of Gaz de France and Suez, which was announced last month. Italian authorities have accused the French of undermining a rival deal for Suez involving the Italian utility Enel.

In a sign of anxiety that the protectionist trend, if uncontained, could damage an already lackluster European economy, the Spanish prime minister, Jose Luis Rodriguez Zapatero, and Villepin were scheduled to meet Monday to discuss a range of issues, including energy, according to an official in Zapatero's office.

EU officials are concerned the government will ensure that a bid for Endesa by Gas Natural, another Spanish utility, will trump a bid by E.ON, even though the German deal is worth about 6 billion, or $7.2 billion, more