The law, which went into effect at midnight Wednesday, was estimated to put than 400,000 people out of work at a time when Russia's economic crisis is deepening and unemployment is rising.
Russian TV said more than 40,000 workers were affected in Moscow alone, at 30 major casinos and some 500 smaller-scale gaming halls and slot-machine parlors. Russian news agencies reported that Moscow police were checking gambling halls across the capital to make sure they were closing.
The law, passed three years ago at then-President Vladimir Putin's initiative, confines gambling to four special zones in far-flung regions of Russia, most thousands of miles away from Moscow.
Despite widely publicized complaints by elected officials about the bane of gambling, it's unclear how much support the restrictions have among regular Russians.
Officials at some of the businesses said they would reopen as market research companies, or rent out their real estate.
Still other businesses were trying to skirt the law by retooling themselves as poker clubs - arguing that should be considered a "game of chance" - or as places for Internet gambling, where patrons place bets but computer servers are located offsite at the distant gaming zones.
Under the new law, casinos and slot machines will be allowed to operate only in Kaliningrad on the Baltic Sea; the Primorsky region on the Pacific coast; the mountainous Altai region in Siberia; and near the southern cities of Krasnodar and Rostov, host to the 2014 Sochi Olympics.
But construction at most of the sites is still in its early stages, meaning it will be months or years before major legal gambling resumes in Russia. Many experts say the law will just drive gambling underground, and criminalize it even more than it already was.