WASHINGTON, April 29 (Reuters) - The White House on Tuesday denounced Amazon's reported plans to disclose the cost that U.S. tariffs imposed by President Donald Trump were adding to its products, and slammed the retail giant for its past ties to China.

White House press secretary Karoline Leavitt said she had discussed the Amazon plan, reported earlier by Punchbowl News, with Trump, and his message about it was: "This is a hostile and political act by Amazon."

The comments sent Amazon shares down 2.2% in premarket trading.

Amazon did not immediately respond to requests for comment on the Punchbowl report or the White House statement.

Trump has imposed a tsunami of tariffs on U.S. trading partners, including China, which has seen tariff costs rise by 145% since Trump took office.

"Why didn't Amazon do this when the Biden administration hiked inflation to the highest level of 40 years?" Leavitt told reporters at a White House briefing.

Leavitt said Amazon's move was not a surprise given a 2021 report by Reuters that the tech company had partnered with a "Chinese propaganda arm."

The White House tweeted a link to the Reuters report earlier Tuesday.

"So, this is another reason why Americans should buy American," she said, underscoring the Trump administration's efforts to shore up critical supply chains and boost domestic manufacturing.