It's dubbed the race that stops a nation, but there are warnings about those "harmless" office sweepstakes.

The glitz, glamour, and horses will be out in force at Flemington for the Melbourne Cup in Australia today.

The Department of Internal Affairs has issued some reminders for businesses wanting to splash the cash.

It says any prize money shouldn't be more than $500, otherwise a license would be required.

Any money raised must be returned as prize winnings and the organiser can't pocket a fee for setting it up.

The department says workplace sweepstakes are legal, but businesses must comply with the rules, or face a fine of up to $1000.

Read the full list of rules here.

However, it says it doesn't collect information about lost productivity during the few minutes the race is on.

The event gets underway at 5pm.