Toll Brothers homeDiego Perez works on a Toll Brothers home this year in Florida.Joe Raedle/Getty Images

Homebuilder stocks were under pressure this week after Toll Brothers issued a warning about a slowdown in the housing market, and an analysis of short interest in the sector suggests there is more pain ahead.

“There has been a recent upswing in short selling in the Homebuilding Sector after short interest in the sector fell by almost a third to $2.96 billion at the end of October,” Ihor Dusaniwsky, managing director of predictive analytics at S3 Partners, a financial technology and analytics firm, wrote in a note on Tuesday.

Rising interest rates have weighed heavily on the group this year, as a jump in borrowing costs traditionally deters first-time home buyers. The Federal Reserve has announced three interest rate hikes so far this year, and eight hikes since late 2015, when the central bank set out to normalize monetary policy following the global financial crisis. As rates have jumped, the XHB, an exchange-traded fund tracking the S&P 500 homebuilders sector, has plunged 21% over the past year.

At the same time, new home sales are declining. The Commerce Department reported last week that new home sales in the US fell 8.9% in October to the lowest level since March of 2016.

Here are the most heavily shorted stocks in the homebuilders sector, according to S3 Partners data.