Former U.S. secretary of state Hillary Clinton (John Gress/Reuters)

The founder of Media Matters, a left-leaning media watchdog group, is joining the Republican National Committee's call for CNN and NBC to halt their plans to produce programming about former secretary of state Hillary Clinton, the organization announced Tuesday.

"Given that this project could coincide with a potential Clinton presidential campaign, the timing raises too many questions about fairness and conflicts of interest ahead of of the 2016 election," writes Media Matters founder David Brock in letters sent Tuesday to the heads of CNN and NBC.