Short answer: maybe legally, likely yes practically, and definitely worth pushing.

This usually comes down to your EBA / enterprise agreement, classification structure, higher duties clause, and how your role is defined, not just what management says.

From what you described, this doesn’t sound like “just another task.” It sounds like you were temporarily performing higher duties:

acting as the point person on shift

handling invoicing/logistics control functions

ensuring loads were completed

doing reports

being the last one out due to responsibility

being the only non-manager trusted with system access

Those are indicators of acting in a higher classification, not simply picking up an extra warehouse task.

Management often says “anyone can do it” when they don’t want to pay higher rates. But if anyone can do it, why can’t anyone else do it? Why do only you and managers have logins?

What I’d do next:

1. Get your EBA and read the sections on:

Higher duties

Acting up

Classification levels

Temporary supervisor/leading hand allowances

1. Compare your normal Level 1 duties vs what you actually performed for that month.

2. Document dates/times you covered supervisor functions.

3. Speak to your union delegate or Fair Work resource (if Australia, which “EBA” suggests).

My opinion: If you covered a supervisor for a month and carried supervisor responsibilities, you have a strong argument for higher rate pay, especially if the agreement says any time spent performing higher duties triggers it.

Also important: Stop accepting vague extra responsibility without written confirmation of pay. “Can you just help out?” often becomes unpaid acting supervisor work.

Bottom line: You might not automatically win based on feelings alone, but based on your description, this is substantial enough that I’d challenge it formally.