The U.S. Justice Department is investigating the hiring practices of technology companies Apple, Google, Yahoo and Genentech, The Washington Post reported June 3.

The companies have been accused of conspiring with each other to prevent other firms from poaching their top staff. Such arrangements are potentially in breach of anti-trust laws.

This is not the first time the Federal Trade Commission has questioned the business practices of these companies, according to a Sacramento Business Journal article. Earlier this year the commission was concerned with the boardroom correlations at the corporations. Google head Eric Schmidt is also a director at Apple Inc., where chief executive officer of Genetech at the time, Art Levinson, also was on the board.

The agreements not to poach staff could breach anti-competition laws if two or more companies formed deals not to pursue the others employees. The hiring practices have been criticised for reducing the opportunities for those company's employees, and practically allows companies to permanently subjugate top staff.