ieExplains: What are tariffs and how do they work?

Mainstream economists are generally sceptical about tariffs, considering them an inefficient way for governments to raise revenue

In the US, tariffs are collected by Customs and Border Protection agents at 328 ports of entry across the country (Noah Berger/AP)

US President Donald Trump’s long-threatened tariffs against Canada and Mexico came into effect on Tuesday.

Imports from Canada and Mexico are now to be taxed at 25%, with Canadian energy products getting tariffed at 10%. In addition, the 10% tariff that Mr Trump placed on Chinese imports in February is doubling to 20%.