Is it permissible for the manager to deduct from the salaries of employees who do not pray with him at the workplace, and what is the ruling on a manager who does not advise them to do so?

It is better for you to pray in congregation at the mosque. However, your congregational prayer at work is permissible according to the majority of scholars. You should advise those who do not pray, explaining the gravity of abandoning prayer, and that the one who abandons it is worse than the fornicator, the thief, the wine-drinker, and the murderer, by the consensus of Muslims, and that he is a disbeliever according to many scholars. If they claim they pray in their homes, explain to them the ruling and virtue of congregational prayer, and that it is an individual obligation (fard ayn) according to the soundest opinions of scholars. If they do not take heed and would be deterred by ostracization, then ostracize them. The manager can threaten them with dismissal if they do not straighten up. However, deducting from their salaries is not permissible, because a hired worker deserves his wage for the work he performs.