Pascal Guyot/AFP Getty Images MEPs slam Commission over US visas Commission breaks EU law on visa rules.

MEPs are losing patience with the European Commission for not forcing U.S. citizens to obtain visas to enter the EU.

The Commission should have imposed the visa requirement in April after the U.S. failed to lift travel restrictions on citizens of five EU countries — Poland, Romania, Bulgaria, Croatia and Cyprus — due to what it told the EU were security concerns.

According to a 2013 law, the EU's executive is required to block visa-free access to the citizens of any country which doesn't waive visa requirements for all EU citizens.

However, no legal action was taken on the grounds that doing so would have "significant impacts" on U.S.-relations since Washington has threatened retaliatory action if visa requirements are reintroduced.

On Wednesday, MEPs are expected to condemn the Commission over the visa issue during a debate in Strasbourg.

"The EU has the right to expect symmetry in its relations with the U.S.," said Polish MEP Kazimierz Ujazdowski. "There is no explanation for the exclusion of Polish citizens and other European countries."

In June, MEPs on the Parliament's Committee on Civil Liberties, Justice and Home Affairs had furious reactions to the Commission's inaction, threatening to take the institution to court for failing to fulfill its legal duties.

"It is absolutely inadmissible that all EU citizens are not treated equally," said Croatian MEP Tonino Picula, who suggested that visa-free access should be "pre-condition" for further trade talks between the U.S. and EU.

Last month, the Canadian government lifted similar restrictions on Bulgarian and Romanian citizens as part of a deal to ratify the Canada-EU trade deal.

"It creates the sense for Bulgarians that for one of our most important partners, the U.S., there are different types of Europeans," said Bulgarian MEP Eva Paunova. "We cannot accept that."

The U.S. Congress has considered removing travel restrictions for Croatia via the "Jobs Originated through Launching Travel" Act, although the law has not been discussed since August.

A spokesperson for the U.S. mission to the EU confirmed that authorities would "continue [their] engagements with these five EU member states to facilitate their work to meet the [Visa Waiver Program's] many requirements."