Yes, generally, you can require employees to have their webcam on during meetings. You may, however, want to take things like low internet bandwidth, equipment failure, software incompatibility, mental health, environmental circumstances, privacy issues, and other reasonable concerns into account when setting expectations. For example, employees may have difficulty staying connected if multiple people in their household are using video conferencing apps at the same time.
I would recommend that you send out some guidelines about video conferencing etiquette. You can include the expectation that employees will participate in meetings using their webcams unless there are extenuating circumstances. Supervisors can then handle, on a case-by-case basis, any issues with employees not using the webcam.