Art Cashin said the benchmark S&P stock index is approaching a key technical level that could spark either big gains or big losses.
Cashin, UBS' director of floor operations at the NYSE, told CNBC's Bob Pisani around midday he expects a "great flirtation" with the S&P's old highs. He sees a significant band of resistance around 1848 to 1851.
"If they approach that and get repelled again you could get a pretty severe pullback... If they get through that you may get some stampede buying from short-coverers and others who say, 'What is it going to take to get this market down? I was wrong. Let me get it back.'"
The bottom line, said Cashin, "If we can break out, that would be great. If we press against it and fail, that could be very troubling."