Casual retail workers will have their penalty rates increased on Saturdays and weeknights, with the boost set to come ahead of the busy Christmas period.

The full bench of the Fair Work Commission, headed by Justice Iain Ross, ruled the Saturday penalty rate for retail casuals should be increased from 10 per cent to 25 per cent.

Casuals starting work after 6pm on weekdays will be brought into line with permanent retail employees, who get a 25 per cent loading on those shifts.

‘In our view, the current casual rates for Monday to Friday evening work and Saturday work lack logic and merit,’ the decision said.

Shop, Distributive and Allied Employees Association national secretary Gerard Dwyer said the changes would benefit more than 350,000 workers covered by the award.

‘These measures go some way to addressing the unjust treatment of casual workers under the award who are not properly compensated for the absence of sick pay, annual leave and the insecurity of work,’ Mr Dwyer said.

The new rates are set to come into place from November 1.

Retailers are fuming over the ‘disastrous’ decision, expressing grave concern for the industry ahead of Christmas trading.

‘Retailers usually thrive during the Christmas period. However, this year I’m concerned many retailers will bear the brunt of an unjust and detrimental decision,’ Australian Retailers Association executive director Russell Zimmerman said.

‘Casual staff are the lifeblood of the retail industry and instead of seeing our retailers shine this Christmas, we will see them undertake more pressure and have to make serious decisions about their Christmas trade.’

The penalty rate increase comes after the commission last year cut retail casuals’ Sunday rates, with those changes to be phased in by July next year.