There has been a huge increase in the number of businesses reporting extortion attempts by drug cartels in Mexico, according to a survey by the American Chamber in Mexico.

The survey of 541 members of the American group as well as the British and Japanese chambers of commerce in Mexico showed the percentage of firms reporting cartel extortions has doubled. Such problems were reported by 18 percent in 2012, but the number jumped to 36 percent this year even as reports of most of other types of crimes declined.

Companies reported fewer thefts of shipments or supplies and fewer threats or attacks on employees in the most recent survey.

Most of the firms surveyed said the overall security situation in Mexico isn't getting worse: 84 percent said their companies were as safe or safer than they were in 2012. However, it was unclear whether that was a result of increased investment by the companies themselves in private security measures or because of a general improvement in public safety.

Twenty-eight percent of the firms said they had hired additional private security forces or consultants over the last year, and security spending averaged about 4 percent of total costs for firms responding in the survey. 

Forty-two percent of companies said they restricted corporate travel by employees in Mexico for security reasons. That is a stance adopted even by the U.S. Embassy in Mexico, which limits nonessential travel by embassy personnel in certain regions of Mexico.

Two percent of companies said they had moved operations out of Mexico for security reasons. Five percent said they had moved, or were considering moving, operations from one Mexican state to another because of security concerns. That is a bit lower than in 2012, when 9 percent said they had moved from one state to another.

The state that lost the most firms was the northern border state of Nuevo Leon, where the industrial hub of Monterrey, Mexico's second-largest city, is located. Monterrey saw a huge increase in drug-related violence starting in 2011.