Just a clarification. It is your card's issuing bank not MasterCard that puts the block on your account. Every bankhas different fraud prevention systems and algoritims designed to ID your spending patterns and put an automatic block when the account is used in a "suspicious" manner. I travel all the time and after calling the Citibank for my first two trips, they got the hint and haven't put a block on me ever. They did call after I spent a month charging away in Spain since this was longer than previous trips - but they did not block it.

Your bank's policy may vary.