Nationals MP George Christensen crosses the floor on penalty rates

A government backbencher has followed through on his threat to cross the floor by supporting a push by Labor to stop cuts to penalty rates.

Nationals MP George Christensen voted with the opposition in the lower house tonight, after the changes were put forward by Labor's employment spokesman Brendan O'Connor.

The move was narrowly defeated 73-72.

The amendments would have given effect to Mr Christensen's private bill - introduced yesterday - to prevent a Fair Work Commission ruling to cut Sunday rates for some workers.

It would have also stopped rates from being cut under enterprise agreements if an employee was worse off than under an award wage.

"Just crossed floor & voted to save penalty rates from Fair Work Commission cuts & unions bargaining them away in EAs. Sad vote lost 73-72," Mr Christensen tweeted.

While the Queensland MP has publicly declared his intention to protect the take-home pay of Australians, it's the first time he has voted against his government on the issue.

He told parliament on Monday he was "breaking ranks" with the coalition because it concerned peoples' livelihoods and ability to put food on the table.

Mr O'Connor said while there were "major deficiencies" in Mr Christensen's bill, Labor's priority was to put workers first.