New York (CNN Business) The advertiser boycott spearheaded by liberal organizations of Fox News host Tucker Carlson is starting to have a visible effect.

Carlson's show, "Tucker Carlson Tonight," was down from the normal five commercial breaks to four on Wednesday night -- a clear sign the pressure campaign spearheaded by liberal activists is having its intended result.

In those four breaks, there were approximately 20 regular commercials, plus six advertisements for other Fox content. In the week before the boycott, Carlson's program averaged 36 advertisements per show, not including commercials for Fox content, according to The Hollywood Reporter

Carlson prompted a backlash last week when he said on his show that mass immigration "makes our country poorer, and dirtier, and more divided." He defended his comments in a segment earlier this week, showing images of trash at the US-Mexico border and arguing border crossers leave behind large amounts of "garbage and waste" as they make their way inside the country.

On Wednesday night's show, Alan Dershowitz, the retired Harvard law professor who regularly appears as a guest on Fox News and other cable networks, confronted Carlson for his rhetoric during an unrelated segment on the latest developments about fired National Security Adviser Michael Flynn.

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