John Richardson - The Reed Amendment And Entering The USA After Renunciation

The Reed Amendment - enacted in 1996 - is found in S. 1182 of the INA - "Inadmissible Aliens". Specifically it says:

(a) Classes of aliens ineligible for visas or admission Except as otherwise provided in this chapter, aliens who are inadmissible under the following paragraphs are ineligible to receive visas and ineligible to be admitted to the United States:

(E) Former citizens who renounced citizenship to avoid taxation

Any alien who is a former citizen of the United States who officially renounces United States citizenship and who is determined by the Attorney General to have renounced United States citizenship for the purpose of avoiding taxation by the United States is inadmissible."

https://www.law.cornell.edu/uscode/text/8/1182

I am aware of only two instances where an a former citizen has been denied entry to the USA because of this.