PHILADELPHIA — Demonstrators and delegates alike loyal to former Democratic presidential candidate Bernie Sanders made it clear on the first day of the Democratic National Convention they are not heeding calls for the party to unite behind presumptive presidential nominee Hillary Clinton.

Hundreds of protesters marched through the downtown streets and outside the Wells Fargo Center, where the four-day convention is being staged, to loudly voice their opposition to Clinton and the Democratic National Committee’s leadership.

A handful of protesters were arrested after trying to scale fences blocking them from the arena, and authorities reported a few protesters were treated for heat-related issues as temperatures soared above 90 degrees.

Scores of protesters outside of the arena, pumped their fists, and chanted in unison “We won’t vote for Hillary!” while, inside the convention hall, Sanders delegates repeatedly jeered and chanted “Bernie! Bernie! Bernie!” when speakers mentioned Clinton’s name. Several wore tape across their mouths that read “Silenced.”

“We don’t want this to be just a hollow show,” said Karen Bernal, a delegate from Sacramento, California.

A coalition of Sanders delegates said on Monday there was growing support among their ranks to contest the nomination of Clinton’s vice presidential running mate Tim Kaine.

At a downtown news conference, Norman Solomon, a national coordinator of the Bernie Delegates Network, a group representing 1,250 Sanders delegates attending the convention, said an informal poll of the group’s members found a majority believed Kaine, a U.S. senator from the swing state of Virginia, was “not acceptable” as a choice.

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Of 300 Sanders delegates who responded to the poll, 251 rejected Kaine, saying his selection did not offer an “olive branch” to liberal leaning Sanders, but instead moved in the “opposite direction,” Solomon said.

“There is very strong overwhelming support for a challenge to Tim Kaine’s nomination,” Solomon said. He did not name any possible nominees the delegates would put forward if they went forward with their protest.

The network represents two-thirds of the roughly 1,900 delegates who pledged their support to Sanders during the drawn-out primary battle with Clinton.

Solomon said Sanders’ delegates “understand that it is essential to defeat Donald Trump” in the general election, but in traditionally Democratic states, many would likely cast protest votes for third-party candidates to signal their disappointment at the Democratic Party’s leadership.

“In swing states hold your nose and vote for Hillary Clinton, in safe states it doesn’t matter,” Solomon said, when asked about the consequences of casting votes against Clinton in a tight race against the Republican presidential nominee.

Several of Sanders’ supporters from the New York delegation said they were still reluctant to support Clinton in the general election, saying they would vote for Green Party candidate Jill Stein or write-in Sanders’s name.

Jesse Rose, 33, a delegate from Astoria, Queens, and a former Sanders campaign volunteer, said he would either vote for Stein or write-in Sanders to send a message to Democratic Party leaders that Sanders’ supporters were still unsettled by the party’s treatment of the Vermont senator throughout the primary race.

Rose said: “At some point the Democratic Party establishment has to get the point that they’re leaving the Left out of the party.”