Warrantless Surveillance and Data Collection:

Under Section 215 of the Patriot Act, also known as the "business records" or "library records" provision, the government can collect a wide range of records, including library records, medical records, and financial records, without requiring a warrant based on probable cause.
This provision has raised concerns that it allows the government to engage in mass data collection, potentially impacting the privacy of innocent individuals.

Use of National Security Letters (NSLs):
The Patriot Act expanded the use of National Security Letters (NSLs), which are administrative subpoenas issued by the FBI without judicial oversight. NSLs can be used to demand records from libraries, internet service providers, and other entities.
Critics argue that the lack of judicial review in the NSL process can lead to overreach and misuse of these investigative tools.

Surveillance of Internet Communications:
Section 215 and other provisions of the Patriot Act have been used to authorize the collection of internet communications and metadata, including email and browsing history.
The extent of this surveillance can be alarming to privacy advocates, as it can potentially lead to the monitoring of individuals' online activities without their knowledge or consent.

Transparency and Oversight Concerns:
Critics point out that certain surveillance activities under the Patriot Act are carried out secretly, such as those authorized by the Foreign Intelligence Surveillance Court (FISC).
The secretive nature of these activities can limit public oversight and transparency, making it challenging for citizens and advocacy groups to understand the full scope and potential abuses of surveillance.

Potential for Racial and Ethnic Profiling:
There have been concerns that the broad surveillance powers granted by the Patriot Act can disproportionately impact minority communities, potentially leading to racial and ethnic profiling.
Critics argue that this can have a harmful and unjust impact on innocent individuals who may be subject to unwarranted scrutiny.

Limited Evidence of Effectiveness:
Some studies and reports have questioned the effectiveness of certain provisions of the Patriot Act in preventing terrorism. Critics argue that the erosion of civil liberties through the act may not be justified by concrete evidence of its success in thwarting terrorist plots.