The Turnbull government is staring down concerted resistance over its combined welfare cuts and childcare package, as crossbench senators threaten to derail the government's No.1 legislative priority before the budget.

A controversial decision to link the "omnibus" savings package - including so-called zombie measures leftover from the 2014 budget - with an overhaul of the childcare system has met with opprobrium from key players.

One Nation leader Pauline Hanson, usually a reliable supporter of the government's agenda, opposes paid parental leave elements in the bill and is among a number of crossbenchers calling for the package to be split.

"I am not sold on the whole lot as a full package," she said on Monday. "I think it may have to be cut up the bit. It is too much in the one bill."