China just sent a clear message to casinos sprouting across Asia: don't peddle your baccarat here.

A Shanghai court on Monday convicted 19 Crown Resorts Ltd. current and former staff of illegally promoting gambling on the mainland, handing out prison sentences of as long as 10 months. While they could have faced a maximum of three years under Chinese law, there was no escaping China's warning to foreign casino operators that see the country's richest citizens as their most lucrative target market.

The crackdown on Australia's largest listed operator was China's broadest enforcement of a law that bars the promotion of gambling on the mainland as authorities seek to halt hundreds of billions of dollars of currency outflows. The convictions coincide with a planned new wave of Asian casinos, from Japan to Australia, that are poised to make a fresh push to attract business from China.