A34 refers to Section 34 of the Immigration and Refugee Protection Act (IRPA), which deals with inadmissibility due to security grounds, including:
- Espionage
- Subversion (e.g., against democratic government)
- Terrorism
- Membership in an organization involved in such act
However, in many GCMS notes, “A34” doesn’t necessarily mean the person is suspected of these things. Instead, it can simply mean the CBSA is conducting an in-depth security screening, especially for nationals from certain countries or if there’s a trigger (e.g., travel history, dual citizenship, past immigration issues, etc.).