WASHINGTON — Amid new tensions with China, the Obama administration on Thursday launched its 15th challenge against Beijing at the World Trade Organization, escalating a long-simmering debate over practices that U.S. officials say limit American farmers’ ability to export rice, wheat and corn to the Asian powerhouse.

The administration says it is trying to hold China to its commitment to allow set quantities of grain and corn to enter the country subject to a lower tariff rate. China agreed to the terms when it joined the WTO, the administration said in a statement announcing new the complaint.

Exporters at times voice concerns that countries make it difficult to gain entry at the lower tariff rates. U.S. trade officials describe China’s system as “not transparent, predictable or fair.”

The complaint comes at a sensitive time in U.S.-China relations. President-elect Donald Trump, a critic of China’s trade practices, angered Chinese leaders when he spoke by phone to Taiwan’s president and later suggested he may reconsider U.S. policy maintaining only unofficial relations with the island, which broke from China in 1949. Beijing has warned that changes to the so-called “One China” policy will threaten stability in the region and damage relations with Washington.

The Obama administration also has expressed frustration with China’s trade practices, though largely through the WTO. The new challenge was the second in recent months. In September, the U.S. alleged excessive Chinese government subsidies for rice, wheat and corn were driving up production from local producers and making it harder for American farmers to export the same crops to China.

United States Trade Representative Michael Froman said China’s policies “limit opportunities for U.S. farmers to export competitively priced, high-quality grains to customers in China.”

“The United States will aggressively pursue this challenge on behalf of American rice, wheat, and corn farmers,” he said.

A Chinese embassy representative in Washington did not immediately respond to an email inquiry seeking comment.

Lawmakers from both political parties applauded the effort in a news release issued by the U.S. Trade Representative’s office. “We have been sounding the alarm, and I am pleased to see USTR taking action to hold China accountable,” said Rep. Mike Conaway, the Texas Republican who chairs the House Agriculture Committee.