U.S. stock-market regulators say they promote transparency and fair play, but this month the Securities and Exchange Commission quietly carved out a China-size exception: When Chinese companies list on U.S. markets, basic auditing rules won’t apply.

Why? Because China’s government doesn’t want them to, and Washington bent to Beijing’s pressure. The SEC has long sought access to the auditing records of Chinese companies suspected of fraud. Tens of billions of dollars in U.S. market value have disappeared in recent years as...