Sen. Bernie Sanders on Friday accused President Donald Trump of likely violating the United States Constitution.

In a series of tweets, the Vermont senator and 2016 Democratic presidential candidate accused Trump of unconstitutionally benefitting from the receipt of 38 new trademarks in China. Some argue that China’s quick preliminary approval of the trademarks violates portions of Article I of the Constitution, known as the “Emoluments Clause.”

“After Trump took office, a whole slew of his trademarks were quickly approved in China. Coincidence? I doubt it,” Sanders wrote. “Receiving preferential treatment for business interests from the Chinese government clearly violates the Constitution’s Emoluments Clause.”

After Trump took office, a whole slew of his trademarks were quickly approved in China. Coincidence? I doubt it.https://t.co/zhgtdhxi3F — Bernie Sanders (@SenSanders) March 10, 2017

Receiving preferential treatment for business interests from the Chinese government clearly violates the Constitution's Emoluments Clause. pic.twitter.com/52rCwMv6Nm — Bernie Sanders (@SenSanders) March 10, 2017

Americans should be confident their president is looking out for their best interests, not his own personal and family business interests. — Bernie Sanders (@SenSanders) March 10, 2017

Thirty-five of the 38 trademarks Trump received were filed under the president’s own name, the Associated Press reports. In February, China agreed to give the Trump Organization the sole right to use the Trump name for construction projects, bringing to end a lengthy legal battle.

While receiving the trademarks itself is not necessarily an issue, legal watchdogs are concerned that China’s government gave Trump preferential treatment, which would violate the Constitution. Critics warn that China expedited the processing of trademark requests and ended its legal battle over the Trump name soon after the president agreed to support the One China policy, or governments’ recognition of the Republic of China but not Taiwan as a separate country. Trump originally questioned the policy.

The Trump Organization holds trademarks in over 80 countries, according to the New York Times, and the president’s companies have filed for more than 120 trademarks in China since 2005. In a statement issued to the press last month, the Trump Organization dismissed the notion that its business dealings in China were a concern.

“Over the last 20-plus years, the Trump Organization has filed trademarks in numerous locations,” the company said. “Although the company will not be doing any new international deals, it will continue to take steps to protect its various brands.”

The White House did not immediately respond to our request for comment on Sanders’ remarks.