MIDTOWN, Manhattan (PIX11) — Don’t say we didn’t warn you.

Get set for massive traffic jams all week long with the opening of the United Nations General Assembly. And before opening day Monday, there was so much Gridlock on Sunday.

One of the big reasons was a march to end fossil fuels.

Traffic on the eve of the United Nations General Assembly is always a nightmare.

Add possibly as many as 75,000 people joining in a march to end fossil fuels, and you have beyond mega gridlock.

It all began with a noon press conference on the West Side with celebrity activists like actress Susan Sarandon.

“What we were asking for is to stop all federal approval for all future fossil fuel projects and phase out fossil fuel on public lands and waters that seems obvious,” Sarandon told the crowd.

From that rally, thousands and thousands tied up traffic in the mid-50s as they headed to the East Side and an even larger gathering blocks from the UN, where Representative Alexandria Ocasio Cortez was the keynote speaker.

“We’re not going to do is have vulnerable communities in a fossil fuel economy left behind,” Ocasio Cortez told the crowd. “We are demanding a change so working people get better jobs and lower bills in a renewable energy economy,” she added.

Organizers and speakers like to point out that those demonstrators are of all ages, colors and races with one shared passion, they said: to save the planet, even if that means creating massive traffic jams.

“I think they should’ve known it was happening, and they should’ve joined us,” Darline Washington, a demonstrator who is also an honors political science major from Howard University, told PIX11 News. “It’s not our fault that the roads were closed.”

Organizers called for all those attending Sunday’s march and rally to join a Monday morning act of civil disobedience at Zuccotti Square in Lower Manhattan.