The AP's "Mexican legislators propose stopping migrants on way to U.S." has the details:

...The bill would allow police or Mexico's migrant-protection agents to designate border areas as temporary "high-risk zones" and declare them off-limits to average citizens.

When high temperatures are forecast, for example, "patrols would go out, inform people of this, and take them to a safe place until it (the heat) is over," Osuna said. After that, the migrants are once again free to go where they wish...

In other words, it's a half-measure. Despite that, it's apparently encountered resistance within Mexico. And, worthies such as the California Rural Legal Assistance Foundation are opposed to it as well.

I note also that at the bottom of the story it gives a link to the Federation for American Immigration Reform. However, they're referred to as, literally, "Federation for American migration". And, that same error is present in other copies of this article (here, here), so I imagine the error was made by the AP itself. It seems to me there's the possibility the AP might run an automated search-and-replace on their articles to replace "immigration" with "migration" or similar. The article itself uses FAIR's correct name, but the words "migrant" or "migration" appear several times in the article...