does the three tier system apply to foreign imported wines aswell ?

If by "the three tier system" you're referring to the cru designation (grand cru, premier cru, deuxieme cru), no, France cannot apply their laws to wines being imported from other countries.

The laws governing wine production are governed by the country/state etc... where the wine is being produced. Laws on importing wine however, are decided upon and enforced by the country who is importing the product. Just as you could have a Premier Cru on your table in the states, the French could have a bottle of $5 California Merlot as long as their government allows it into the country. The wine laws in France and much of the wine making world serve to preserve the history & heritage, as well as to control the quality of the product.