BET founder and billionaire Robert Johnson is lobbying the Congressional Black Caucus to endorse Sen. Clinton as the vice presidential nominee.

WASHINGTON (CNN) — Billionaire businessman Bob Johnson, a close adviser and friend to Sen. Hillary Clinton , launched a campaign Wednesday to persuade Sen. Barack Obama to offer the vice presidential slot on the Democratic ticket to Clinton.

Johnson told CNN's "American Morning" that Clinton knows about his push but "she didn't direct me to do it."

A day after the final two primaries, Johnson sent a letter to House Majority Whip Jim Clyburn on Wednesday to lobby the Congressional Black Caucus to endorse Clinton as Obama's running mate. He said it needs to be done for the sake of party unity.