U.S. Trade Representative Katherine Tai announced Monday that China will not adhere to the so-called “phase one” trade agreement signed under President Donald Trump, according to sources who spoke with Kayla Tausche.

Sources said that China has failed to live up to the promise of the deal, which required it to buy an additional $200 billion worth U.S. products over the next two years.

It will be the Biden Administration’s most aggressive pushback against China. Tai will speak Monday in Washington about the China trade policy.

Uncertain how the USTR might respond. CNBC has been told by sources that USTR was considering potential sanctions against China in light of its non-compliance.

Trump signed the agreement in 2019, and Tai’s Monday speech will be the final three months. This agreement calls for China’s expansion of purchases from certain U.S. services and goods between Jan. 1, 2020 and Dec. 31, 2021.

China’s purchases of U.S. exports through August are estimated to be running at about 62% of the trade deal’s targets, Chad Bown, a senior fellow at the Peterson Institute for International Economics in Washington, told Reuters.