A think tank founded by a notorious anti-Muslim activist is planning to co-sponsor an upcoming rally against the Iran deal headlined by Republican presidential candidates Sen. Ted Cruz (R-TX) and Donald Trump.

Cruz and Trump announced Thursday that they were planning the joint event to voice their opposition to a landmark agreement to curb Iran’s nuclear program. Tea Party Patriots, the Center for Security Policy and the far-right Zionist Organization of America were expected to sponsor the rally, which is scheduled for Sept. 9 on Capitol Hill, according to The Washington Post.

The Center for Security Policy is an anti-Muslim think tank founded by former Reagan administration official Frank Gaffney, who often speaks about the threat of creeping Sharia law and has accused Republican and Democratic officials alike of being Muslim Brotherhood plants in the U.S. Cruz spoke via video link to an event Gaffney’s organization put on last month in the first-in-the-nation primary state, the New Hampshire National Security Action Summit.

Gaffney also endorsed Trump’s hardline immigration platform last week on the Center for Security Policy’s blog.

“Robust immigration stances have fueled Donald Trump’s meteoric rise in the polls,” he wrote. “If they wish to catch him, his many rivals must do no less.”