Forget what Federal laws say, If they were not adopted by the state you live in, or if they were adopted with amendments, they may not apply as originally written. Remember, Federal laws do not apply in all states here, unless the individual states adopt them.
I think all states obey what the federal Hacienda laws state. Jalisco laws do demand that all contracts and advertising be in pesos.
You can't have a contract in the U.S. in currencies other than dollars unless it is an international contract, so I don't know why people in MX think that MX doesn't want contracts in pesos. Paying in dollars, especially by check, is usually a way around taxes