Compliance halts are individual stock halts that can be initiated either by the regulatory bodies that oversee the US markets such as the SEC (Securities Exchange Commission) and FINRA (Financial Industry Regulatory Authority), or by individual exchanges such as NYSE or NASDAQ.
Securities can be halted for a variety of issues that stem from non-compliance with regulatory statutes. Some of these include: stock delisting, unusual trading activity, or failure to file necessary forms or disclosures.