The executive branch conducts investigations, issues subpoenas and certain agencies can directly hold you in contempt if you don't respond to a subpoena others can ask a court to find you in contempt of court. After all the FBI, DEA, ATF, CBP among many more law enforcement agencies are part of the executive branch.
> The executive branch conducts investigations,
>> Essentially, the Court held that the Constitution's text implies a power to investigate given its power to legislate.
> issues subpoenas
>> the U.S. Supreme Court clarified Congress's power to issue subpoenas in a 1917 case (Marshall v. Gordon), stating that "in virtue of the grant of legislative authority there [was] a power implied to deal with contempt."
> certain agencies can directly hold you in contempt
>> The authority of Congress to cite an individual with criminal contempt is found in Title 2, Section 192 of the U.S. Code.
> others can ask a court to find you in contempt of court
>> Either chamber of Congress may start the process in a committee (such as the House Judiciary Committee) and may rely on the legislative counsel's office like the Office of Senate Legal Counsel for help drafting a contempt resolution. Once the resolution is drafted and voted out of committee, it then goes to the full House or Senate (depending on where it originates) for a simple majority vote.
https://www.findlaw.com/litigation/legal-system/contempt-of-...