EU officials have strongly criticised US attempts to re-open a 2007 deal on exchanging personal information of trans-Atlantic air passengers.
Estonians could have visa-free travel to the US this year
The United States has recently offered several EU countries visa-free travel if they agree to tougher restrictions.
Although citizens from some European countries do not need a visa, many newer EU member states are excluded.
EU Justice Commissioner Franco Frattini said it was unacceptable that the US had tried to reach separate accords.
European Commission spokesman Jonathan Faull said that if the United States did not move soon to include all EU countries in the visa-waiver programme, the EU could adopt a visa requirement of its own for US citizens.
"We have been extremely patient... but our patience can't last forever," he said.
In June last year, the EU agreed that 19 categories of personal information on passengers flying from Europe to the United States would be supplied to the US Department of Homeland Security. which could be kept for 15 years.
Two months later, the US Congress passed new rules, calling on the US government to consider requiring European countries to adopt additional measures such as allowing air marshals on planes as part of the visa waiver programme.
EU VISA-WAIVER COUNTRIES
Ireland, Portugal, Austria, Italy
Belgium, Slovenia, Denmark, Luxembourg
Spain, Finland, Sweden, France
Netherlands, Germany, United Kingdom
Although it is up to national governments to decide on the deployment of air marshals, the EU is frustrated that the US has gone directly to individual governments to discuss other proposals which are for Brussels to negotiate on member states' behalf.
One controversial measure is for passengers to fill in an application form on the internet.
"We're over there and we're meeting with a number of European counterparts," a US Homeland Security Department spokesman said on Tuesday.
The Czech and Estonian governments have confirmed they have been in talks with US officials, but they insist they are taking EU law into account.
By the end of the year, Czechs and Estonians along with Greeks could all benefit from visa-free travel to the US.
The commission has said it will raise the issue with member states at a very high level in the coming days.