Mexico’s Senate has approved a measure that would legalize the sale and use of marijuana.

To become law, Mexico’s lower house still needs to debate and pass the legislation. And while it would represent one of the most significant national legalizations to date, some pro-legalization groups are raising concerns about its potential impacts.

“This legislation is totally designed to put the cannabis market into a few hands,” said Julio Salazar, an attorney with the group Mexico United Against Crime, which is pro-legalization.

It would also make it difficult for everyday citizens to use and grow their own marijuana. He hopes the legislation can be improved as it moves through the Chamber of Deputies.