The US Internal Revenue Service is to solicit the help of the world’s top accounting firms in its widening effort to clamp down on offshore tax evasion.

The IRS is planning to speak on Tuesday to six accounting firms about how they could help find foreign banks that fail appropriately to identify US customers holding investments or income in offshore accounts, according to people briefed on the plan. A conference call has been scheduled between the agency and Deloitte, Ernst & Young, KPMG, PwC, Grant Thornton, and BDO Seidman, they say.