On Wednesday, Icahn accused the giant money management firm of pumping air into a bubble in high-yield debt by pushing seemingly safe investments on individual investors that were actually filled with what he claims are risky bonds. At one point, Icahn compared what BlackRock (BLK) is doing today to what the banks did in 2007 when they sold billions of dollars of faulty subprime mortgage bonds.

“They are putting their name on this stuff and people are buying it,” said Icahn. “Blackrock is an extremely dangerous company.”

Icahn made the comments while sitting next to BlackRock CEO Larry Fink on stage at the Delivering Alpha investment conference, which is put on by CNBC and Institutional Investor magazine. Icahn honed in on BlackRock’s sale of high-yield exchange traded funds. He said the ETFs offer the appearance of liquidity, making the high-yield bond market seem safer than it is.

Icahn also noted that BlackRock’s ETFs often get exposure to high-yield bonds through credit default swaps, which he suggested would make the liquidity problem even worse, but he didn’t explain how. A recent prospectus for BlackRock’s $13 billion iShares iBoxx High Yield Corporate Bond ETF (HYG) makes no mention of its use of CDS. A spokesperson for BlackRock said the fund is not invested in CDS. The fund does hold some cash, along with high-yield corporate bonds.

But a BlackRock mutual fund that also invests in high-yield bonds, the BlackRock High Yield bond fund (BHYAX), does use derivatives to get some of its exposure to such securities. At the end of the first quarter, the fund had nearly 8% of its portfolio in CDS and bond index funds, including the iShares high-yield ETF, which could ostensibly cause some liquidity problems if both funds needed to sell at once.

It’s not the first time Icahn has sounded the alarm on high-yield debt, a market that he claims is overvalued. Icahn said on Wednesday he expected there to be losses in oil and gas high-yield bonds.

Others have worried about the influence that BlackRock has on the market because of its size. Last year, shortly after BlackRock hit $4 trillion in assets, Fortune’s Carol Loomis wrote an in-depth profile of the firm and Larry Fink. (Read: BlackRock: The $4.3 trillion force)

Fink agreed that there could be some losses in high-yield debt. But he said that he didn’t see a crash coming, and that he didn’t see similarities between the market today and what it was like in 2007. “There isn’t nearly as much leverage in the system as we had then, particularly at the banks,” said Fink.

Fink noted that Icahn’s criticism of his firm was baseless. He said BlackRock offers lots of investment options and that the firm doesn’t tell investors how to invest. And he also said that a number of studies showed that ETFs increased liquidity in the markets, not the opposite.

“I would be happy to buy Carl lunch sometime and explain it to him because I don’t think he gets how ETFs work,” said Fink.