The top executive of Nasdaq OMX Group Inc. said Monday that the Obama administration will have a difficult time implementing a plan to curb the trading activities of Wall Street banks.

Determining what constitutes proprietary trading by banks, versus positions taken on behalf of customers and other forms of hedging, appears "impossible," according to Nasdaq OMX Chief Executive Bob Greifeld.

The administration last month unveiled a plan to impose sweeping restrictions on banks' trading for their own accounts, in a bid to protect the broader financial system from the risk of heavy trading losses at any one bank.

"It's a hard job for them to do," said Greifeld, on a conference call discussing Nasdaq OMX's fourth-quarter results. "I think they have to find a different path."

Subscribe Now

Access to authoritative analysis and perspective and our data-driven report series.

14-Day Free Trial

No credit card required. Complete access to articles, breaking news and industry data.