Meanwhile, the theft of information about some 40 million credit-card accounts in America, disclosed on June 17th, overshadowed a hugely important decision a day earlier by America's Federal Trade Commission (FTC) that puts corporate Americaon notice that regulators will act if firms fail to provide adequate data security.
a day earlier 是时间副词作状语,修饰介词短语 by America's Federal Trade Commission。说明“美国联邦贸易委员会(FTC)前一天作出的决定”,而整个 a day earlier by America's Federal Trade Commission 是作decision 的定语。