This week Saudi authorities resumed a sweeping crackdown on foreign workers violating local labor laws. Officials arrested more than 20,000 people over two days, according to the Jeddah-based Saudi Gazette, and deported many of them. The crackdown, which King Abdullah had suspended in July for six months to allow time for workers to regularize their status, primarily targets workers who do not have valid residency or work permits, but also affects workers with valid documents who are not working for the employer the documents designate.

Why, in a country that so tightly regulates its foreign workforce, do so many workers risk arrest and deportation by working illegally?

For many workers the answer is simple: they have little control. The Saudi labor regulation system gives employers inordinate power over workers by making the employers responsible for maintaining the validity of their employees’ residency and work permits. If they fail to do it, the worker pays the price.

And no foreign worker in Saudi Arabia is allowed to change jobs without the approval of his or her designated “sponsor,” or employer, making it extremely difficult for workers to leave when an employer fails to pay them or subjects them to abuse.

If the labor system is so abusive, why don’t the workers just leave and go home?

They can’t, not without an official “exit visa” signed by the worker’s employer. This, in combination with employers’ standard practice of confiscating workers’ passports, leaves workers with no way out, often forcing them to work in horrific conditions, which sometimes even amount to forced labor– or else to violate the law by working somewhere else off the books.

Given these bleak options, it shouldn’t be surprising that so many workers resort to under-the-table jobs.

If Saudi Arabia is serious about bringing workers into legal compliance, the kingdom should focus less on arresting and deporting workers and more on reforming the abusive labor system that pushes them into the shadows.