The customs notice came in a letter addressed to Carney, which Trump posted on his platform Truth Social. The 35-percent general tariffs are set to take effect on August 1.
In the letter, Trump refers to the tense situation between the neighboring countries, where Canada has not backed down.
"Instead of cooperating with the US, Canada responded with its own tariffs," Trump writes.
According to Trump, Canada's trade policy has caused an "unsustainable trade deficit against the US". He also repeats his previous criticism that Canada is not doing enough to stop fentanyl smuggling into the US.
"If Canada cooperates with me to stop the flow of fentanyl, we will, perhaps, consider adjusting this letter. These tariffs can be changed, upwards or downwards," Trump writes.
Mark Carney writes in a response on the platform X that Canada has always prioritized protecting domestic jobs and businesses during trade negotiations with the US and intends to continue doing so.
According to Carney, Canada has made "important progress" in stopping fentanyl, while focusing on building a strong Canadian economy.
"We are strengthening our trade partnerships around the world," Carney writes, referring to the fact that the country has begun to look more towards Europe, for example, since the trade conflict with the US broke out.
The letter to Carney is the latest in a series of threatening tariff letters that Trump has sent this week. Over 20 countries have received letters – and Brazil is the hardest hit, with potential tariffs of up to 50 percent.