The iShares iBoxx $ High Yield Corporate Bond ETF (NYSEArca: HYG) and the SPDR Barclays High Yield Bond ETF (NYSEArca: JNK), the two largest high-yield corporate bond exchange traded funds, as well as rival junk bond funds have come under increased scrutiny in recent weeks as investors have pulled away from speculative-grade debt and bond-related exchange traded funds, pushing up yields on junk bonds.

The BofA Merrill Lynch high-yield index is trading at about 600 basis points higher than government bonds. However, if energy, metals and mining debt is excluded from the high-yield index, the spread is about 80 basis points less. Additionally, if commodity producer debt is excluded, the junk bond index has a yield of 6.7%.

The commodity producers make up a good chunk of the junk bond ETFs. For instance, HYG includes 12.5% energy.

Looking ahead, the Federal Reserve could add more pressure on the junk bond market. Fed Chair Janet Yellen has stated that higher rates are coming this year, and analysts expect more selling as rates go higher. Other problems are mounting.

“For the first time in more than 20 years, U.S. speculative-grade bonds are set to post a fourth straight month of losses, topped off by a decline of more than 2.3 percent this month alone, Bank of America Merrill Lynch Indexes show. More than half the sectors in the $1.3 trillion market have reported negative price returns for five months, a streak not seen since the 2008 financial crisis,” reports Sridhar Natarajan for Bloomberg.

Slumping oil prices remain an issue for junk bond funds. Industry experts warn that more oil-and-gas companies are poised to follow the recent Samson Resources Corp. bankruptcy filing as oil prices remain low after the steep drop off that began last year, the Wall Street Journal reports.