BRUSSELS, Jan 21 (Reuters) - U.S. customs authorities

will face a real challenge if President Donald Trump goes

through with his threat to place tariffs on six EU countries -

rather than the whole European Union - given the ease of

movement of goods between EU members.

Trump has vowed to place increasing tariffs on goods from EU

members Denmark, Finland, France, Germany, ‌the Netherlands and

Sweden, as well as non-EU states Norway and Britain, until the

United States was allowed to buy Greenland.

TECHNICALLY POSSIBLE, BUREAUCRATICALLY COMPLEX

Under EU ​rules, goods manufactured in the bloc are only

marked as being of EU origin, but a ‍third country can require

information is provided by individual EU members.

It can be ⁠difficult to determine that ⁠a good is made in a

single EU member, however, because of extensive cross-border

supply chains and the ability to transport goods from one ‌EU

member to another without customs controls. Establishing the

origin of ​goods would be a complex task for U.S. customs

authorities.

Niclas Poitiers, research fellow at Bruegel, said it would

probably not be difficult for smaller companies to obscure the

production location ⁠of their products, while larger firms with

more transparent ‍supply chains ​might decide to shift production

to EU countries not targeted by the measures.

CAN U.S. TARGET BRANDS?

Brand names are generally associated with specific

countries, but production can take place elsewhere.

Carmaker Volkswagen, for ‍example, manufactures cars in

Germany, but also in Slovakia, while Sweden's Volvo Cars has a

factory in Ghent, Belgium with a similar capacity to the plant

at its Gothenburg headquarters, which makes Volvo's top-selling

XC60.

Volvo has shifted output following tariffs. It will start

making the XC60 in the U.S. at the end of the year and has

increased production of electric vehicles in Belgium after the

EU placed tariffs on China-built EVs, but ​the timeframe ‍for such

switches has typically been at least a year.

WHAT ABOUT FRENCH WINES AND CHEESES?

Well-known EU foods and drinks, such as French champagne or

Camembert, may be more easily targeted because ​they are marketed

and sold in ways that highlight their heritage and origins.

Reinforcing this, the European Union has a system of

"geographical indications", or GIs, granting intellectual

property rights to some 4,000 products linked to particular

areas of production, from Italy's Parma ham to Spain's Manchego

cheese and Greece's Kalamata olives. As a result, the term

"champagne", for example, can only be used for a sparkling wine

made in the Champagne region in the northeast of France or

"feta" for a specific ​cheese from Greece.

The United States has repeatedly denounced the system as

protectionist, particularly when it is included in the EU's

trade agreements to ensure foreign partners also agree to

respect the protected status of a range of products.

Of the six targeted countries, France has ‍the most GIs.