The advice comes as Havier Hughes, who runs the Pilley Stores branch in Lymington, Hampshire, is accused of stealing almost £20,000 in 2009. Royal Mail has since terminated his contract and he is due to appear in court next month.
A Royal Mail spokesman said: "We very much welcome hearing from subpostmasters about any financial concerns they may have. All of our subpostmasters are able to contact us freely and we would always seek to provide advice and support where possible."
In the past year several subpostmasters have been found to have siphoned money from the post office to pay debts from their store. In March Graham Warnes was found guilty of stealing £28,000 over two years to keep his Hertfordshire store afloat. He received a suspended sentence and was able to pay back the money with help from locals.
In January Clive Lewis of Pant Post Office in South Wales was sentenced to a year in prison after pleading guilty to stealing more than £37,000 to pay bills and staff wages.