Shares of AMC Entertainment Holdings Inc. /zigman2/quotes/200235402/composite AMC +3.39% slumped 1.1% in premarket trading Tuesday, after the movie theater operator disclosed a stock offering of up to 15 million shares. The company said the stock will be sold "from time time, through an 'at-the-market' offering program." The number of shares in the program would represent roughly 14% of the shares outstanding. The disclosure comes a day after the biggest U.S. cinema chain said it will resume operations at several New York state cinemas starting Oct. 23. The stock has tumbled 51.1% year to date through Monday, while the S&P 500 /zigman2/quotes/210599714/realtime SPX -0.16% has gained 6.1%.