Fox News anchor Sean Hannity urged witnesses in the Russia investigation to delete evidence and destroy their electronics before giving them to Robert Mueller.
Hannity's advice seemed at least partly sarcastic, suggesting that Hillary Clinton would get away with such tactics while regular people would not.
Destroying or altering court evidence is a criminal offense under US federal law, punishable by up to 20 years in prison.
Mueller reportedly asked witnesses to hand over their phones so he could inspect their conversations on encrypted messaging apps.
The witnesses reportedly complied with Mueller's request.
It came after former Trump campaign manager Paul Manafort was accused of witness tampering.
Sean Hannity has called on the witnesses in Robert Mueller's investigation to delete their evidence and destroy all their hardware in an attempt to derail the probe.
The Fox News host said on Wednesday night that witnesses should "acid-wash the emails on the hard drives and your phones" then smash them into "itsy bitsy pieces" with a hammer.
The advice — which would be illegal to follow — appeared to be at least partly sarcastic, and was delivered as part of an attack on Hillary Clinton.
Hannity's point appeared to be that Clinton could get away with destroying evidence, while allies of Donald Trump could not.
Here is a full transcript of what Hannity said:
"Meanwhile as the Mueller witch hunt churns on, the Special Counsel — this is interesting. They are demanding that witnesses turn in their phones so Team Mueller — and of course, his pitbull Andrew Weissmann and Jeannie Rhee, who worked for Clinton, get to review all of their electronic communications.
"He wants the phones turned over. Even texts that are on what are called encrypted apps like WhatsApp or Signal or one of these things. And they need Mueller's witnesses... I don't know.
"If I were to advise to follow Hillary Clinton's lead: Delete all your emails and then acid-wash the emails on the hard drives and your phones, then take your phones and bash them with a hammer to little itsy bitsy pieces, use BleachBit, remove the SIM cards, and then take the pieces and hand them over to Robert Mueller and say: 'Hillary Rodham Clinton, this is equal justice under the law.'
"How do you think that would work out for everybody who Mueller's demanding their phones of tonight? I'm certain the result would not be the same as Hillary's."
Destroying or altering evidence is a criminal offense under US federal law and can result in up to 20 years' imprisonment.
Hannity's segment came in response to reports that Mueller had asked witnesses to turn in their personal phones so he could inspect private messages on encrypted messaging apps like WhatsApp, Signal, and Confide.
The witnesses have handed over their phones to avoid a subpoena, CNBC reported, citing unnamed sources.
The request came after Mueller's office accused Paul Manafort of attempting to communicate with potential witnesses in the probe via phone and encrypted messaging apps.
A federal judge will decide whether to revoke or revise Manafort's bail on June 15.