A Chinese education company backed by U.S. investors including Kobe Bryant is cracking down on how its Western teachers cover politically fraught topics.

VIPKid, one of China’s most valuable online education startups, has put hundreds of its mostly American teachers on notice for using certain maps in their classes with Chinese students, and has severed two teachers’ contracts for discussing Taiwan and Tiananmen Square in ways at odds with Chinese government preferences, people familiar with the company say. Since last fall, teachers’ contracts state that discussing “politically contentious” topics could be cause for dismissal, according to one reviewed by The Wall Street Journal.

The moves highlight the balance a Chinese company must strike in fulfilling global aspirations while toeing Beijing’s line. Five-year-old VIPKid is currently in talks to raise as much as $500 million in new funding from U.S. and other investors that could value the company at roughly $6 billion, people familiar with the fundraising said.

“A company must keep good relations with the government and ideology,” said Peter Fuhrman, chief executive of investment firm China First Capital . “But that can cause friction when you’re also courting foreign investors, expanding business overseas and employing a large American workforce.”

Beijing-based VIPKid says it has more than 60,000 teachers in the U.S. and Canada who teach English to more than 500,000 children ages 4 through 15, who live mostly in China. Teachers work as independent contractors and can earn between $14 and $22 an hour. They must have a bachelor’s degree, at least one year of teaching experience and eligibility to work in the U.S. or Canada.