Liberal senator Eric Abetz has dramatically intervened in the penalty rates debate, calling for workers' existing rates to be protected, and creating a fresh political headache for Prime Minister Malcolm Turnbull.

In an opinion piece for Fairfax Media, Senator Abetz has publicly called on the Fair Work Commission to protect existing pay rates so "no worker is worse off" and only new employees would be paid reduced rates on Sundays and public holidays.

Senator Abetz said he supported the landmark decision to cut penalty rates for certain workers in the retail, hospitality and tourism sectors because it would help small business and create jobs, but the decision "had to be implemented in a fair and equitable manner".

His comments will likely be seized on by Labor, which has demanded Mr Turnbull intervene to stop the pay cut.