What do critics say is an important problem related to the North American Free Trade Agreement?

Answer 1

The classic response is "unsafe working conditions".

However, in real life NAFTA has created many issues due to lack understanding of microeconomics and how economic integration would affect the common man. It seems the only country that has been fully benefited from the treaty has been Canada -- this however, is open to debate.

In the case of Mexico, sudden imports of highly-subsidized American and Canadian agricultural products have put out of business many small-scale farmers, who were forced to migrate into the cities or into the United States. This is also a big problem for the United States, as these migrants (often illegal) represent a social issue, but keep prices of agricultural products down. This has become a vicious circle between the U.S. and Mexico.

In the case of the United States, many industries are leveraging cheaper labor costs and laxer environmental and working laws, migrating into northern Mexico to establish assembly plants known as maquiladoras. These inject much-needed dollars into the Mexican economy, but at a high price, including exploitation of the local workforce and environmental damage. These of course, also mean fewer industrial jobs are available for the United States workforce.