A strict immigration policy has helped make Japan one of the world's oldest and most homogeneous societies. Now, Prime Minister Shinzo Abe's plan to invite as many as half a million foreign workers is testing the country's tolerance for change.

Abe is preparing to introduce legislation to allow migrants to start filling vacancies next year in sectors worst hit by the country's shrinking population. While the government hasn't released a target, local media including Kyodo News have reported numbers that would represent a 40 percent increase over the 1.3 million foreign workers now living in the country.

In a sign of urgency, Abe's government has announced an April start date for the policy even before debate has begun in the Diet. The proposal is among the first he's seeking to tackle after winning a historic third term as head of the ruling Liberal Democratic Party last month, paving the way for him to become the country's longest-ever serving prime minister.