The European Union threatened Wednesday to hit American diplomats where it hurts _ with new visa restrictions _ if Washington doesn’t stop dragging its feet on lifting visa requirements for 12 EU nations.

The retaliatory measures against U.S. diplomatic passport holders would begin next year.

The majority of the EU’s 27 countries are included in the U.S. visa-waiver program, but citizens of a dozen mostly eastern European countries still need a visa to enter the United States.

Some of those nations have signed bilateral deals with Washington that should allow them visa-free travel in the near future, but the EU is unhappy about the slow progress of the negotiations.

Greece and all countries that have joined the EU since 2004, except Slovenia, are currently excluded from the visa-waiver program, meaning their citizens must apply for visas at U.S. embassies or consulates ahead of their trip _ and can be turned down.

The U.S. visa waiver program, created in 1988, was originally focused on preventing illegal immigration. But since Sept. 11, 2001, the focus has shifted to security, and the program has been altered several times in hope of strengthening America’s ability to prevent terrorism.