More investors are betting against electric-car maker Tesla than any other U.S. stock, new data show.

The dollar amount of shares shorted on Tesla increased 28 percent in the last month to $10.7 billion, according to S3 Partners. The percentage of Tesla's available stock currently sold short exceeds 25 percent, according to FactSet.

"Tesla, which was overtaken by Apple as the largest U.S. equity short recently, is back on top of the league tables, a position it has held since March 2016," wrote Ihor Dusaniwsky, head of research at S3 Partners. "Tesla short sellers, after reducing their short exposure for the first two months of 2018, have reversed course and shorted Tesla stock heavily over the last five weeks."

Tesla offered no comment for this story.