Crossbench powerbroker Senator Nick Xenophon has called for a review of the federal lobbying register and code of conduct, as several lobbyists back widening the register's coverage.

The register, established in 2008 under the Rudd Government, was promoted as an effort to bring transparency to the lobbying industry, particularly in light of the "WA Inc" scandals involving former West Australian premier Brian Burke.

ANU emeritus professor of political science John Warhurst wants the lobbying register expanded.

But the register and its associated code of conduct only covered third-party lobbyists and Australian National University Professor John Warhurst told Fairfax Media that at most it covered a third of all lobbyists working the corridors of power.

Other groups, from unions and industry associations to in-house government relations staff at major companies, religious entities, non-government organisations and charities, were exempted on the grounds it was clear who they were acting for.