Barnaby won't throw stones in glass house

Deputy Prime Minister Barnaby Joyce has refused to criticise a Nationals colleague for crossing the floor and voting with Labor over penalty rates.

It's hard for a leader to criticise a colleague who crosses the floor of federal parliament when you were once yourself a serial offender.

That's Barnaby Joyce's take after Nationals backbencher George Christensen sided with Labor over penalty rates.

The maverick Queensland MP on Tuesday supported an opposition amendment that would have prevented cuts to Sunday penalty rates for some workers.

Mr Joyce, standing beside Mr Christensen and the whole Nationals team on Wednesday, insists his party believes in the liberty of the individual more than any other in Parliament House.

"Do you ever find it strange that no one in the Greens ever crosses the floor," he told reporters in Canberra.

"They were all born like peas in a pod."

Unlike the Nationals, Labor members who cross the floor can also be expelled, he said.

"George is part of our team. How can I criticise George? It's not like I didn't do it myself."

When Mr Joyce was a Nationals senator he crossed the floor 28 times.