A controversial trial of drug testing welfare recipients will almost certainly be postponed after the Turnbull government conceded it was unlikely to win sufficient support from the Senate crossbench.

The trial was to have applied to new welfare recipients from January 1, 2018, but Social Services Minister Christian Porter on Wednesday indicated he was prepared to excise the trial from omnibus welfare legislation so other measures could be approved by Parliament before the end of the year.

"The sticking point, fundamentally, in the legislation has been the drug testing trials for welfare recipients. The bill is critical," Mr Porter told the National Press Club in Canberra.

"So the bulk of that bill, which reforms the compliance system, is so critical to what we are trying to achieve that I wouldn't want to sacrifice the bulk of that in terms of timeliness while we are still negotiating around drug testing."