Three Nationals senators crossed the floor this week partly out of frustration with their Coalition counterparts.

On Wednesday afternoon, backbenchers Barry O'Sullivan, Matthew Canavan and John Williams supported a housing affordability motion from Family First senator Bob Day.

It was defeated 48 votes to 10 with most Government senators, Labor and the Greens voting against it.

WA Liberal Chris Back also crossed the floor.

The ABC has been told the Nationals senators made the decision at the last minute and did it partly because they like Senator Day.

But Government sources said the move was also designed to send a message to the Liberal Party.

"Stop walking over me to get to f****** Lambie is the obvious message", one said.

"Don't forget the Nats are their own party. Even the Queensland ones."

"They want to be consulted. Not ignored in favour of the crossbench," another said.

Backbenchers are allowed to cross the floor without fear of repercussion.

Agriculture Minister Barnaby Joyce crossed the floor 28 times during his tenure as a Queensland senator.

But some Liberal senators were unhappy with the decision of the three Nationals.

The housing affordability motion was largely symbolic.

It urged the Senate to condemn "the deliberate restriction of land for new housing and subsequent price gouging by state and territory land management agencies", and highlight, "the constraints on land supply which are the principal causes of worsening housing affordability".