At work and In force

At work adjective - On the job.

In force and at work are semantically related in active topic. In some cases you can use "In force" instead an adjective phrase "At work", when it comes to topics like having movement.

In force adjective - Exerting force or influence.

At work and in force are semantically related in active topic. You can use "At work" instead an adjective phrase "In force", if it concerns topics such as having movement.