VLADIVOSTOK, Russia—Wearing a Nike coat and an Adidas hat, a North Korean laborer waited with 60 compatriots to board a flight home from this city in Russia’s Far East.

After three years of construction work, the laborer, Mr. Ri, was returning with $600, after his pay was docked for missed work due to an injury. He said he would miss his life in Russia, where he enjoyed watching the South Korean news on his mobile phone—until his North Korean handlers confiscated it three months ago to deter defections.

“At least I’m taking back some money from Russia. I won’t receive anything working in Pyongyang,” Mr. Ri said.

Hundreds of North Korean laborers are streaming out of Russia every day, thinning out a workforce that once stood at 30,000. Only several thousand remain. On most days this month, North Korean airline Air Koryo flies twice from Vladivostok to Pyongyang, up from twice a week earlier this year.

The exodus was mandated in 2017 by the United Nations Security Council. Tightening sanctions in response to North Korea’s launch of an intercontinental ballistic missile, the Security Council barred countries from issuing new worker permits and said they would have to expel the regime’s workers within two years. That deadline arrives on Sunday.