Under siege from a rampaging Turnbull government and an exodus of members, Australia's once mighty trade unions are secretly examining radical changes including dollar-a-week memberships in a bid to survive and then regain their industrial and political clout.

In what would be an extraordinary departure from more than a century of practice, senior union figures are urging a fundamental rethink of what union membership means which could see dues slashed to as little as a dollar-a-week, as well as half-memberships at cut rates, and even individually tailored services for an increasing disaggregated and isolated workforce in which many people "have no employer" per se.

Prime Minister Malcolm Turnbull renewed his warning to Senate cross-benchers to pass the government's Australian Building and Construction Commission bill. Credit:Andrew Meares

Exclusive collective bargaining agreements where only members benefit from any hard-won pay rises and other improvements are also being examined.

The ideas are among many canvassed in a confidential draft policy paper intended for the ACTU and obtained by Fairfax Media.