(CNN) Beto O'Rourke signed a pledge to turn away donations from fossil fuel industry executives Wednesday, moving to blunt criticism that has dogged his bid for the 2020 Democratic presidential nomination.

The former congressman from Texas rejected contributions from lobbyists and political action committees this year and during his 2018 Senate run. But he has faced persistent questions and criticism at campaign events -- often from university students -- about why he accepted donations from individual oil and gas industry executives.

"We returned any money we received over $200 from any fossil fuel company executives. We will not take that money going forward," O'Rourke said Wednesday in a video recorded from his front porch in El Paso and posted to Twitter.

"And we continue to try to be the largest grass-roots campaign in this country -- all human beings, all fellow Americans, all focused on the same goals, including confronting climate change before it is too late," he said.

I have signed the No Fossil Fuel Money Pledge. Here's why: pic.twitter.com/VtuJQeMMgT — Beto O'Rourke (@BetoORourke) May 1, 2019

The pledge comes the same week O'Rourke rolled out a $5 trillion plan to combat climate change , with a goal of net zero greenhouse gas emissions by 2050.

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