U.S. Citizens used to be charged a hefty entry tax upon crossing into Argentina until March of 2016. At that time the reciprocity fee $160 USD was suspended for 90 days and it remains suspended for now until further government notice.
The entry tax called a reciprocity fee was put in place in Argentina to charge citizens of countries who charge Argentinians large visa fees to enter their countries. Notably among these are Canada and Australia who have not been granted this exemption.
The Argentinian measure of good will comes as they are expected to be granted greater access in the US visa waiver program in 2017. US citizens entering Argentina have the right to stay for up to 90 days on the now visa free/fee free policy. If you happen to be visiting Argentina now is a great time and eliminations of these types of rules are always victories for travelers who are looking for greater cooperation among nations. We most certainly will be thanking the immigration authorities on our upcoming visit.