When Tina Liu was hired to teach literature in a public elementary school in southern China, her contract included the usual warnings about absenteeism and job performance.

Then came another line: Traveling abroad without the school’s permission could get her fired.

The rule was reinforced in a staff group chat. “According to regulations from higher-ups, teachers need to strengthen their disciplinary awareness,” the message said. “We will currently not permit any overseas vacations.”

Across China, similar warnings are spreading as the authorities tighten control over state employees’ contacts with foreigners. Some kindergarten teachers, doctors and even government contractors and employees of state-owned enterprises have been ordered to hand in their passports. Some cities make retirees wait two years to reclaim their passports.

In many cities, travel overseas by public employees, even for personal reasons, requires approval. Business trips abroad for “ordinary research, exchange and study” have been banned. And in most provinces, those who have studied abroad are now disqualified from certain public positions.

Officials cite various reasons, including protecting national security, fighting corruption and cutting costs. But the scope of the restrictions has expanded rapidly, sweeping up employees who say they have no access to sensitive information or government funds. The New York Times spoke to seven public employees, including an elementary school music teacher, a nurse and a literature professor, who confirmed the restrictions.