Yes, if structured correctly: they must be limited as to territory, duration, and type of work, based on an interest worthy of protection, and reasonable. Unlimited bans are deemed invalid — we build the structure around the case law.
Turkish law puts numbers on “reasonable”: under Articles 444 to 447 of the Code of Obligations a non-compete binds only where the employee had access to the customer base or to production secrets; it may not normally exceed two years, and it must be confined by place and line of work. A court can trim an overbroad clause rather than strike it out — so a tightly drawn ban is far more useful than a sweeping one.
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