Why are airplanes heading west slowed by the jet stream?

When an airplane is let's say going from New York to Los Angelis, The pattern of wind and weather is east to west, The airplane is going the opposite way of the way the Earth and wind are moving. That's why when you go from LA to New York, it takes less time! 

Jet streams are heavy winds and the airplanes must work to fly against the heavy wind current

This act gave the federal government the power to relocate any native in the east to territory west of the mississippi river.