"They could end up funding the disaster that is the NBN."

Less than two weeks ago, Nationals leader Warren Truss said he expected the opposition to push amendments to protect the Communications Fund.

"[The Communications Fund] is likely to go to failing Labor states and territories to fund infrastructure projects that in some cases were originally promised last century. Meanwhile, rural and regional people will suffer, as they have done right through Rudd Labor's first year in power," Truss said.

Nationals Queensland senator Ron Boswell was one of four party members to cross the floor, along with two Liberals and a raft of abstaining members. Only five Liberals voted for the move.

Boswell said in a written statement the move was a deal-breaker with the bush.