The tariff applies to some Vietnamese exports of cold-rolled steel sheets, although if the groups can prove the steel comes from a country other than China, they are exempt from the tariff, according to a declaration from the economy ministry published in Mexico's official gazette.

Vietnam's largest steelmaker, Hoa Phat, is subject to a nearly 12% tariff while Posco Vietnam will face a 26% tariff, though the country of origin exemption also applies to them.

A number of nations have in recent years raised alarm at Chinese steel producers selling their surplus abroad at below-market rates, a practice known as dumping, with some attempting to circumvent "anti-dumping" measures by first shipping the steel to other countries.

In August, Mexico hiked a tariff to 25% on some steel imports from countries with which it does not have a free-trade agreement, including China.

The tariff published on Thursday brings a government anti-dumping investigation opened at the behest of steelmaker Ternium's local unit nearly two years ago to a close. Ternium declined a request for comment.

The United States has also expressed concern about its own imports of steel and aluminum products from Mexico, where the U.S. alleges a "lack of transparency" regarding their country of origin.

Steel production in Latin America has dropped in recent years as imports have grown. The region is expected to produce 83% of the steel it consumes this year, according to November data by regional association Alacero.

China is the region's No. 1 steel supplier, accounting for nearly a third of what is brought into Latin America, according to Alacero.

Brazilian steelmakers also have requested their country's government impose a 25% tariff on Chinese steel imports, though little action has been taken.

"The government is not in the mood to create friction with the Chinese," industry group head Carlos Loureiro said earlier this month, as China is one of Brazil's largest trading partners.

(Reporting by Kylie Madry; editing by Barbara Lewis)

By Kylie Madry