Well, the The Colorado Supreme Court ruled that the 2008 raid of the local tax preparer's office aimed at building identity-theft cases against hundreds of suspected illegal immigrants violated their Fourth Amendment right to privacy. From The Denver Post:
The 4-3 ruling was the latest and most devastating legal blow against Operation Numbers Game, an investigation launched by Weld County Sheriff John Cooke and District Attorney Ken Buck that aimed to use tax returns to identify and prosecute illegal immigrants.
The raid on Amalia's Tax and Translation, a business that caters to Spanish-speaking clients, led to the seizure and review of some 4,900 tax returns. Deputies said they found about 1,300 suspects in identity-theft and criminal-impersonation cases.Prosecutors around the country have been watching the case closely, reportedly the first in the United States in which law enforcement sought to use tax returns — generally considered confidential under federal law — to take suspected illegal immigrants to criminal court.
The court majority ruled that the defendant in this case, Ramon Gutierrez, as a taxpayer "has a reasonable expectation of privacy in his or her tax returns and return information, even when that information is in the custody of a tax preparer."
The ruling also said that Gutierrez, who was among more than 70 people charged with criminal impersonation and identity theft, was a victim of an "exploratory search" and that police had no probable cause to search Gutierrez's tax records.