Delegates for Bernie Sanders at the Democratic National Convention are planning to fight the nomination of Virginia Sen. Tim Kaine as the party’s vice presidential nominee.

At a news conference Sunday, Norman Solomon, a Sanders delegate from California and national coordinator of a group of Sanders delegates called the Bernie Delegates Network, said Kaine’s positions on a range of issues were unacceptable to Sanders supporters.

Solomon said presumptive Democratic nominee Hillary Clinton’s selection of Kaine as her running mate showed “demonstrable contempt for the progressive wing of this party.” Sanders delegates, Solomon said, object to Kaine’s stances on trade agreements, labor laws and what they view as an insufficient commitment to fighting climate change.

“This is an assault on the progressive base of the Democratic Party in the number of 13 million voters,” said Solomon, referring to those who voted for Sanders in the Democratic primaries. He added that “this struggle is about whether we will accept a dystopian future” that “perpetuates a situation of massive oligarchy dominating our economy and politics.”

According to a straw poll of 285 Sanders delegates held by the Bernie Delegates Network, 88 percent called Kaine “unacceptable” as Clinton’s running mate. Solomon said the Sanders camp would have preferred more outspoken progressive voices such as Massachusetts Sen. Elizabeth Warren or Ohio Sen. Sherrod Brown.

To protest Kaine, the delegates will try to hold a vote on his nomination on the convention floor. Solomon said there were also discussions about protesting Clinton’s speech accepting the nomination either by walking out, turning their backs toward her or remaining silent throughout the speech. Some 45 percent of pledged delegates at the convention support Sanders.

Speaking Sunday on NBC’s “Meet The Press,” Sanders said he would have preferred Warren over Kaine as Clinton’s running mate. Sanders praised Kaine’s character but said “His political views are not my political views.” Sanders did not endorse Clinton until earlier this month after she had wrapped up the nomination in June.

Solomon spoke the day after the publication by WikiLeaks of internal emails from the Democratic National Committee that appeared to show its staff supporting Clinton over Sanders, contravening its pledged neutrality. Solomon called that neutrality a “fiction.” He called a leaked email that proposed questioning Sanders’ Judaism and belief in God “shameful.”

“Sadly, it speaks for itself,” Solomon said of the email. “This is the progressive Democratic National Committee? It’s just shameful.”