A prized spot in next month's $3 million Caulfield Cup is on offer to the winning horse in the MRC Foundation Cup.

And the winner of Saturday's Group Three race at Caulfield will also earn its associated charity $20,000.

As part of the MRC Foundation race day, the horses in the feature race of the day will run for different charities.

The winning horse will earn its charity the largest share of a $30,000 prize pot.

Caulfield RSL Welfare Fund, one of 16 organisations involved, earned the right to be first to select a horse and aligned with race favourite The United States.

Six-year-old The United States will be one of a host of horses in the race trying to cement a Caulfield Cup.

The Robert Hickmott-trained The United States is the $3.80 favourite for the race, previously been run as the Naturalism Stakes.

Last year's winner Trust In A Gust won for Down Syndrome Victoria with the charity represented this year by another Darren Weir-trained runner, Taiyoo.