To blame everything related to manufacturing moving to Asia on Unions is shortsighted.

Are manufacturing unions and their demands responsible for manufacturers moving to China? - Quora

Look at this logically. Decades ago, there were plenty of both union and nonunion factories in the United States. If unions were the cause of the jobs going to China, we would only see the union factories closing and the nonunion ones would still be in business.

Only partly — in general, union or non-union, manufacturing wages in the US far exceed wages in S Korea, China, etc. So manufacturing moved off shore and will stay off shore. We cannot compete with peasants in India.

Probably the biggest reason why manufacturing moved to Asia and Mexico/Central and South America is due to the United States government interference in and regulation of free enterprise capitalism.

Unions may be part of the problem but most likely is the greed of management wanting to lower costs to improve profits. If profits increase then shareholders are happy and bosses have more time to seduce secretaries.