At a 10th anniversary party for "Hardball" last week, Chris Matthews said that Bush White House officials -- especially some in Dick Cheney's office -- had tried to "silence" him by putting pressure on executives at MSNBC.

Matthews' comments were a little cryptic, but now he's elaborating in an interview with TV Guide. Matthews says that there was a "concerted effort" -- carried out by three people linked to Cheney -- to kill discussion of the role Cheney's office played in trumpeting a supposed nuclear threat from Iraq.

"I thought on the 10th anniversary it would be good to celebrate the First Amendment, which gives us all our living," Matthews tells TV Guide. "We reviewed in brief the remarkable experience of covering the Clinton [scandal] and the defense of the war with Iraq. And the difference in these two cases was that although I was extremely tough on Clinton, there was never any attempt to silence me -- whereas there was a concerted effort by [Vice President Cheney's office] to silence me. It came in the form of three different people calling trying to quiet me."

TV Guide asks Matthews why he's "coming out about this now."

"I think people ought to know this," he says. "There's a lot going on among our producers, our young bookers, now that I never noticed before. There is an almost menacing call that you get whenever someone hears something they don't like -- their people call up and threaten, or challenge, and get very nasty. That's now become the norm. I told people, 'Just tell me this from now on.'

"Every time someone calls and tries one of those things, whether it's the Mitt Romney campaign or the John McCain campaign or whatever, I will put it on the air. I'm tired of this kind of pressure that's now become normal among the young staffers on these campaigns. When it's coming from the vice president’s office -- there was a concerted effort to stop me from reporting on what the vice president's office was doing in terms of making the case that there was a nuclear threat from Iraq. I wanted to remind people [that] having a talk show that is outspoken is not without its troubles."