When smoking—which must occur outside company premises—you're no longer "at the disposal of the employer" (Article L 3121-1 of the Labor Code). This time is deducted from your working hours. Check your collective bargaining agreement and company rules for entitled breaks. Log time in and out.
Executives typically face fewer restrictions. Review your contract: most feature flexible hours with flat daily pay. Employers can't penalize completed work due to breaks (unless excessive).
Theoretically, yes—for excessive breaks. But labor courts (prud'hommes) may deem it moral harassment. With judges highly attuned to this, employers rarely act.
Insights from Agathe Lemaire, Paris Bar Lawyer.