In the wake of industry concentration and the occasional firm failure, the issue of a credible alternative industry structure has been raised. The limiting factor on the expansion of the Big Four to include additional firms, is that although some of the firms in the next tier have become quite substantially large, or have formed international networks, effectively all large public companies insist on having an audit performed by a Big Four network. This creates the complication that smaller firms have no way to compete well enough to make it into the top end of the market.