Peso weakens 1.33 percent to 19.44/dollar - its highest level in over a month - following the decision.
The peso has been hit by fears a Fed hike could push investors out of emerging markets, as well as concerns US Republican presidential hopeful Donald Trump could win elections on Nov. 8.
Mexico's peso weakened more than 1.7 percent on Tuesday after opinion polls showed Trump, who has made disparaging comments about Mexicans, had closed the gap on Democratic opponent Hillary Clinton ahead of the election.
Speaking on national television on Wednesday, Mexican Finance Minister Jose Antonio Meade said intervention to support Mexico's peso does not make sense when volatility is caused by global concerns, like jitters regarding the US election.