In the wake of a $2.2 billion arms deal between the United States and Taiwan, China has vowed to stop doing business with US companies that sell weapons to the autonomous island that Beijing still considers to be part of it’s sovereign territory.

In a Monday statement, a spokesman of China’s foreign ministry said that “China’s government and Chinese companies will not cooperate or have commercial contacts with these US companies.” A day earlier, Chinese state media had published a list of US firms that may be subjected to Chinese sanctions. China has not outlined how it aims to implement the sanctions.

Beijing announced similar measures in 2010 and 2015, but it is not clear if these actually went into effect and if so, what their impact on US firms has been.

Read more: China says will freeze out US companies that sell arms to Taiwan