Investor Carl Icahn is making good on his promise to "push hard to oust" Yahoo CEO Jerry Yang from his position. He has sent another letter to Yahoo's current board blasting Yang and the directors for failing with strategic growth plans.

According to Reuters, Icahn's latest letter states: "While Google's income from operations grew 59 percent per year for the last two years, Yahoo's income from operations shrank 21 percent.

"What was the board doing during this period? Where was their great plan? Why did you permit Google to leave you in the dust?"

Icahn, who recently amassed a stake in Yahoo, launched a proxy bid for the company in May, just after Yahoo beat back Microsoft's hostile takeover bid. In an open letter to the Yahoo board at that time, Icahn disputed Yang's claim that Yahoo would be better off without Microsoft.

Last week, Icahn continued his tirade when he told The Wall Street Journal in an interview about his intent to push hard to oust Yang.

"I am amazed at the lengths that Jerry Yang and the board went to entrench themselves in this situation," Icahn told The Journal. 

The investor's final showdown with Yang is expected later this summer at Yahoo's annual meeting, which is scheduled for Aug. 1.