Thousands of ultra-Orthodox gathered at the entrance to Jerusalem Sunday for a massive protest against plans to introduce compulsory military service to the Haredi community.

Carrying placards calling to rise up for the “Torah of Moshe” and declaring they would never submit to a Knesset bill that would dramatically increase IDF service among the ultra-Orthodox communities, protesters began demonstrating outside the capital’s convention center even before the official 4 p.m. start time for the rally.

Many wore sackcloth, symbolizing mourning for the creation of the law, following decades during which the ultra-Orthodox were able to claim an exemption from army service.

Some 3,500 police and other personnel were set to secure the massive demonstration, which is expected to draw hundreds of thousands, making it one of the largest in the country’s history.

Organizers billed the event as a “million-man protest” and a prayer rally.

The Magen David Adom rescue service said it had upped its readiness level to prepare for the crush of demonstrators at the event near the entrance to the capital.

The demonstration will close off one of the city’s main transportation hubs, and is expected to bring much of the capital to a standstill.

By 3 p.m. traffic issues had rippled outside the capital, with heavy congestion reported on area highways.

Police said the demonstration would snarl traffic, close roads and shut down public transportation around the entrance to the city and the Knesset.

Route 1, the main road between Tel Aviv and Jerusalem, closed after 2 p.m. Sunday from the Latrun area to the capital, and the Jerusalem Central Bus Station also shut down in the afternoon, along with much public transportation in the city.

“We have no intention of the large demonstration turning into a riot,” police official Yossi Frianti told Ynet. “We have coordinated with the protesters that there won’t be riots and we hope they stand by it.”

Shas party chairman Aryeh Deri, one of the most vocal leaders of the protest against the emerging draft bill, on Saturday night called on the ultra-Orthodox public to refrain from engaging in violence against police. “I beseech the young people,” he said. “Please, I beg of you, heaven forbid there should be any desecration of God’s name… There may be provocations… be careful.”

In the past, ultra-Orthodox protests over the draft issue have turned violent. Earlier this month in Ashdod, a protest that drew several hundred led to over a dozen arrests for rioting.

A major proponent of the Haredi draft, Economy Minister Naftali Bennett, came out against the demonstration on Saturday night, asserting that “military service is not a ‘decree’” – as some ultra-Orthodox leaders have been referring to it – “but rather a big mitzvah.”

He instructed members of his Jewish Home party to refrain from attending the demonstration, an apparent nod to MK Moti Yogev, who said he was thinking of going.

Jerusalem’s Deputy Mayor Yisrael Kellerman, one of the organizers of the event, said he hoped attendance would be in the hundreds of thousands. “We wanted to bring the Haredi community from the entire country,” he told the ultra-Orthodox news site Kikar Shabbat. “There were some difficulties because within a few short days we had to bring everyone — we have to bring thousands of buses.”

The latest version of the draft bill has faced scathing criticism from ultra-Orthodox leaders over its inclusion of individual criminal sanctions against draft-dodgers that would kick in if the community as a whole failed to meet rising quotas for the draft. But it has also faced criticism from proponents of an equal draft for delaying such criminal sanctions until mid-2017, after the next election.