Federal authorities are examining whether Chinese companies deliberately restricted the world's production of storage containers for the shipping trade just before the COVID-19 pandemic began six years ago, sources with knowledge of the probe told CBS News. 

Investigators have been looking at a handful of Chinese firms that together control the majority of unrefrigerated shipping container manufacturing around the globe, the sources said.

The companies in late 2019 slowed production by restricting the number of hours employees worked, which the investigators believed indicated a conspiracy to cut global supply and inflate prices, two of the sources said.

Spokespeople for the Justice Department didn't immediately comment.

The companies' alleged moves came just before the global supply chain came under enormous strain.

China reported the first cluster of COVID-19 cases in December 2019 and the outbreak spread in early 2020. 

According to the U.S. International Trade Commission, in the second half of 2020, the number of shipping containers in circulation was "insufficient to meet customer storage demands and higher than anticipated consumer demand for imports." The commission said that "unexpected recovery in demand shocked the distribution system." 

Several Chinese executives have been indicted, two of the sources said. The Department of Justice was expected to unseal the indictment Tuesday. 

The action comes days after President Trump returned from Beijing for the first presidential visit to China since 2017, when Mr. Trump visited during his first administration. 

Though the trip was short on major breakthroughs, the president touted "fantastic trade deals." He announced an agreement by China to purchase at least 200 Boeing aircraft, more U.S. oil, as well as more soybeans and other agricultural products.

Xi said that during the summit, he and Mr. Trump reached "common understandings on maintaining stable economic and trade ties" and on expanding cooperation, according to Chinese state news agency Xinhua.

Sources told CBS News that one of the Chinese container manufacturing executives was taken into custody in France about three weeks ago and remains in detention. Officials intend to have him extradited to the United States.

Trump administration officials sought to keep the case from becoming public until after the president's summit, two of the sources said.