By Alison Sider and Ted Mann

The Trump administration threatened Wednesday to bar mainland Chinese airlines from flying to and from the U.S. starting June 16, saying Beijing has failed to approve resumption of these routes by U.S. carriers.

Some U.S. airlines have sought to resume service to China this month, after suspending flying there earlier this year as the coronavirus pandemic took hold.

The U.S. Transportation Department said Wednesday that the Civil Aviation Administration of China hasn't approved requests by United Airlines Holdings Inc. and Delta Air Lines Inc. to resume flights. It accused China of violating an agreement that governs air travel between the two countries.

Chinese carriers continued to fly passengers between the U.S. and China even after U.S. carriers had stopped flying in February and March, albeit at reduced levels. Currently four Chinese airlines -- Air China Ltd., China Southern Airlines Co., Xiamen Airlines and China Eastern Airlines Corp. -- operate scheduled passenger flights between the two countries, the Transportation Department said.

The order blocking Chinese carriers is set to go into effect June 16, but President Trump could opt to put it into effect sooner. A White House spokesman declined to comment on whether the president would do so. The order doesn't affect Hong Kong, only mainland Chinese carriers, a spokesman for the Transportation Department said.

The threat of a shutdown in direct flights was the latest sign of souring U.S.-China relations that are at their worst in more than three decades.

Both sides struck a trade deal that promises to boost Chinese purchases of U.S. farm products. Administration officials said in February that China was abiding by the terms of the first phase of a trade deal that took effect that month, including a $32 billion increase in Chinese purchases of American grain over two years. China meanwhile announced it would begin excluding some American goods from tariffs that had been slapped on during the escalating trade war that marked the first 2 1/2 years of Mr. Trump's presidency.

But many other business issues, including market access, investment and technology, have become points of contention.

The airline issue strikes at a central tenet of the Trump administration's China policy----the need for reciprocity in relations that the administration says have been tilted in Beijing's favor. As a result, both governments have expelled reporters from the other's country, and the Trump administration last week said it is scrutinizing Chinese firms listed on U.S. stock markets.

A senior administration official said Wednesday that while the move on airlines wouldn't have much practical impact on travel, with most flights flying at minimal capacity, the threat showed how the Trump administration was focused on reciprocity in its dealings with China. "If they keep escalating, we're going to keep escalating," this official said.

Write to Alison Sider at alison.sider@wsj.com and Ted Mann at ted.mann@wsj.com