The US Republican Party voted Friday to deny two US television networks rights to carry presidential primary debates if they don't abandon planned documentaries on Democrat Hillary Clinton.
NBC Entertainment is planning a miniseries and CNN is working on a documentary about the former secretary of state as she mulls a potential run for the White House in 2016.
The Republican National Committee voted unanimously to go through with a threat it first made last week.
"That's why we said to the media, with a united voice, that a network that spends millions to spotlight Hillary Clinton is a network with an obvious bias," RNC chairman Reince Priebus said at a party meeting in Boston.
"And that's a network that won't be hosting a single Republican primary debate," he said.
"There are plenty of other outlets. We'll still reach voters, maybe more voters. But CNN and NBC anchors will just have to watch on their competitors' networks," Priebus added.
Clinton, a former first lady and US senator whose turn as America's top diplomat earned her widespread praise, is seen as the clear Democratic frontrunner for president.
She has made no announcement of her political plans but the RNC move -- more than three years ahead of the 2016 election -- show the party's nervousness about a run by Clinton, who narrowly lost the Democratic nomination to Barack Obama in 2008.
Friday's decision is the first step in a Republican bid to re-exert control over the primary process, which was considered too long in the 2012 campaign that led to Mitt Romney winning the nomination.
Many conservatives Republicans want the party to skirt the networks altogether and organize the debates itself, with "appropriate" moderators, according to the resolution adopted Friday.
The Republicans would thus be able to reduce the number of debates and change the tone.
There were 20 held in 2012 to whittle down a field of some 10 contenders. This was too many, according to a party report published in March.
"The number of debates has become ridiculous, and they're taking candidates away from other important campaign activities," said the report, dubbed the party "autopsy" after Obama defeated Romney in 2012.
The goal is to organize 10 or 12 debates starting in September 2015, or just five months before the first caucuses and primaries, in Iowa and New Hampshire.