The Mexican Government has passed a new anti-money laundering law which went into effect September 14, 2010. With this new law, the use of American Dollars (CASH) to make purchases in Mexico will change. Other payment methods such as credit cards of all types and all issuing banks, Travelers Checks, Mexican pesos and non-American foreign currencies (such as Euros or Canadian Dollars) are NOT affected in any way by this new law.
The most noticeable differences will be: Hotels,Exchange Booths, and local banks will only be able to change a maximum of $1,500 USD CASH per person per month into Mexican Pesos. Previously there was no limit. Businesses (including restaurants and shops) will only be able to accept a maximum of $100 USD CASH per transaction - but the number of transactions per customer is not restricted. Certain businesses may not be able to, or may choose not to accept US Dollars for any purchase at all (this may include shops, etc), however still accepting Mexican Pesos.
If a customer wants to purchase an excursion (for example) that costs $150 US dollars per person, customers will only be able to pay $100 of this amount in USD CASH and the remainder will need to be in another form of payment (credit card, Mexican pesos, etc). Airlines are advising that within Mexico, they will only accept Mexican Pesos and credit cards for any fees (including baggage fees). Vacationers should never carry large amounts of American dollars with them abroad, but instead they should consider either using a credit card or ATM card to withdraw Mexican Pesos.