At a speech at the Royal United Services Institute today, on the eve of the Nato Summit, Mr Fallon will warn that the United States will not go on "picking up the cheque" if Europe chooses to prioritise social welfare spending over defence.
At a one-day conference at the think tank, Mr Fallon will call for Britain's Nato allies to increase their investment in national defence, saying: "Nato was formed on the basis that Europe would pay her way. Like any insurance policy, defence only pays out when you pay in.
"US taxpayers won't go on picking up the cheque if we choose to prioritise social welfare spending when the threats are on our doorstep."
Mr Fallon's comments will echo those made by Foreign Secretary Philip Hammond, who warned that Nato must show it still has the political will to fight back in the event of a Russian attack on any member of the alliance.