US President-elect Donald Trump posted on his Truth Social platform Monday that on Jan. 20, as one of his first executive orders, he will sign all necessary documents to charge Mexico and Canada a 25 percent tariff on all products coming into the US. He also said that China will face 10 percent tariffs above any existing tariffs.

This shows his will to implement strong protectionist trade policies right from his inauguration day. International trade rules are expected to be jolted.

Trump said the move will be in retaliation for illegal immigration and crime and drugs coming across the border. In other words, he intends to use tariffs as a tool to solve non-economic issues.

Mexico, China and Canada are the top three suppliers of goods to the United States, accounting for more than 40 percent of its total goods imports. Because the supply networks of South Korea are intertwined with the three countries, Seoul should try to minimize side effects of any tariffs on the countries.

If China's exports to the US decrease, so will its demand for South Korean intermediate goods which are used to make other products. South Korean companies doing business in Mexico and Canada will be hit directly. Higher tariffs will raise prices of goods that South Korean companies produce in Mexico and Canada and export to the US. In Mexico, Samsung Electronics and LG Electronics run electric home appliance factories and Kia produces cars in Mexico for the US market.

South Korean battery and related companies are currently building their factories in Canada. Some of the companies are reportedly reviewing whether to diversify their production bases to other countries, but it is difficult to implement the option readily due to many other variables.

If China finds it noncompetitive price-wise to export its goods to the US due to tariffs, it will turn to other markets such as Southeast Asia and the Middle East. Then, South Korea will encounter tougher competition there from China in the fields where they are already competing, such as steel, petrochemicals, textiles and displays.

It is noteworthy that Trump promised to put tariff pressure even on Mexico and Canada, which are parties to free trade agreement with the US. During his first administration, Trump pushed for the United States-Mexico-Canada Agreement, which replaced the North American Free Trade Agreement. Many US imports from Canada and Mexico are exempted from tariffs because of the USMCA trade agreement. He has touted the passage of the USMCA as a highlight of his presidency, but tariffs on the countries if enacted would be tantamount to nullifying the USMCA. This is an act of showing his "America first" principle bluntly.

It would be naive to believe South Korea, whose trade surplus with the US was the eighth-largest among its trade partners as of late September, would be off Trump's radar. South Korea has concluded a free trade agreement with the US, but considering Mexico and Canada, it is questionable whether South Korea can bet on the FTA remaining unscathed.

There is a view that Trump is likely to impose higher tariffs on China and Mexico, while using them as a bargaining chip in negotiations with other countries over non-tariff issues. And yet, Seoul should prepare countermeasures just in case. South Korean companies have been able to achieve considerable exports to the US partly thanks to the FTA, which enhanced the price competitiveness of South Korean goods. If the comparative advantage weakens or vanishes, South Korea's exports to the US will likely be greatly set back. Companies need to consider increasing production on the US soil instead of exporting via third countries.

As tariff barriers go up, the role of the government becomes important. The government should highlight that South Korean companies have invested heavily in the US. It is necessary to present mutually beneficial deals proactively to Washington in the fields that could arouse Trump's interest, such as shipbuilding, nuclear power plants and semiconductors. The government should try to ensure that the Trump administration will have a positive view of South Korea.