Protesters have also set up a tent city in a park below the Parliament building in Jerusalem.

After a late-night emergency meeting, the country’s main labor union said it was considering a general strike, in rare coordination with the country’s largest alliance of business leaders. And a group representing 10,000 military reservists said its members would resign from military duty if the overhaul goes ahead without social consensus — adding their names to a smaller group of 1,000 Air Force reservists who made a similar threat on Friday.

The reservists’ warnings have led to fears within the defense establishment about Israel’s military readiness. The Israel Defense Forces, or I.D.F., are heavily reliant on reservists, particularly the Air Force.

Citing these fears, a group of 15 retired army chiefs, former police commissioners and former directors of the foreign and domestic intelligence agencies wrote a public letter to Mr. Netanyahu on Saturday night, calling him “the person directly responsible for the serious damage to the I.D.F. and Israel’s security.”

Hours later, the prime minister began experiencing an irregularity in his heart. It was detected by a heart-monitoring device fitted at Sheba less than a week ago, after Mr. Netanyahu was rushed to the hospital following what one of the doctors at the hospital described on Sunday as a fainting episode.

At the time, Mr. Netanyahu’s office said he had experienced mild dizziness, and the doctors said he was suffering from dehydration after being out in the sun during a heat wave. But he was kept in the hospital overnight, underwent tests in the cardiac department and left with an implanted heart monitor.

The data from the device was “an indication for urgent pacemaker implantation,” according to Prof. Roy Beinart, the director of Sheba’s department of rhythm disturbances and pacing. Pacemakers are usually inserted into the chest area through a small incision and are designed to regulate a person’s heartbeat and prevent problems that could end in cardiac arrest. Small pacemakers can also be fitted without a chest incision and with a minimally invasive procedure.

Gabby Sobelman contributed reporting from Rehovot, Israel.