Alberta-based oil and gas producer Nexen  will lay off 400 workers, the company announced Tuesday.

Nexen is a wholly-owned subsidiary of CNOOC Limited, one of China’s major national oil companies.

The company said it would reduce its North American workforce by 340 employees, and affiliate Nexen UK is working to reduce its staff by 60.

About 40 of the total job cuts will occur in the United States, a spokeswoman said. Nexen’s only U.S. offices are in Houston, according to its website.

Nexen CEO Fang Zhi attributed the cuts to the dramatic downturn on the energy sector.

“While regrettable, these organizational changes are necessary to align the company with our reduced capital spending program,” Zhi said in a statement. “We take these decisions seriously, and all impacted employees have been treated fairly and with respect.”

CNOOC completed its purchase of Nexen in 2013 for $15.1 billion.

The company has offshore operations in the North Sea, West Africa, the Gulf of Mexico and Trinidad & Tobago. It also operates in the Canadian oil sands. It has shale gas interests in British Columbia, Colorado, Wyoming and Texas, as well as Colombia.

At the time of the transaction, some lawmakers from both the U.S. and Canada questioned the deal, saying they worried about giving foreign governments a stake in their natural resources.

After Canadian authorities approved CNOOC’s acquisition, they vowed to reject any future foreign takeovers of oil sands assets.