The killings took place at a prison camp near the town of Tal Afar, some 90 miles east of the Syrian border or 260 miles north-west of Baghdad, legislator Mahma Khalil said.
Mr Khalil said he spoke to four different people with knowledge of what happened inside of the camp, though a reason for the killings on Saturday was yesterday still not apparent.
“The militants want to spread horror among them to force them to convert to Islam or to do something else,” Mr Khalil said.
He added that those killed included men, women and the elderly. He said he believes that thousands other Yazidis are still held in that camp.
The latest killings follow the shootings of 300 Yazidi hostages on Friday. The Yazidi Progress Party announced on Saturday that 300 Yazidi hostages were killed late Friday in Tal Afar.
Osama al-Nujafi, Iraq’s vice-president, said that the reports of the mass slaughter were “horrific and barbaric.”
Kurdish outlet Shafaq News also reported on the killings, describing the news as a “heinous crime.”
Qulu Sanjiri, a member of the commission, said that at least 3,000 Yazidis are still being held by the group.
An official of the Kurdistan Democratic Party said: “Women, children and elderly people are confirmed among the victims. IS gathered them in one place and shot them all together.”
The Yazidis, followers of an ancient faith, are regarded by Islamic State as infidels.
Tens of thousands of Yazidis fled in August when the Islamic State group captured the northern Iraqi town of Sinjar, near the Syrian border. But hundreds were taken captive by the group, with some Yazidi women forced into slavery, according to international rights groups and Iraqi officials.
About 50,000 Yazidis – half of them children, according to UN figures – fled to the mountains outside Sinjar during the onslaught. Some still remain there.
The US launched airstrikes and humanitarian aid drops in Iraq on 8 August partly in response to the crisis on Sinjar mountain. Since then, a US-led coalition of countries has conducted airstrikes across Iraq in an effort to destroy the Islamic State group, which now holds a third of both Iraq and Syria.
The Sunni militant group views Yazidis and Shiite Muslims as apostates deserving of death, and has demanded Christians either convert to Islam or pay a special tax.
Previously, the group has let go of hundreds of other Yazidis held in captivity. Iraqi and Kurdish officials said they believe the militants could not afford caring for the prisoners, many of whom were elderly and sick.
In March, the United Nations Human Rights Office published a report describing the savage killings, torture, rape and sexual slavery of Yazidis by the Islamic extremists
The jihadists consistently separated out men and boys over the age of 14 to be executed, according to investigators.
Younger boys were forced to become child soldiers and women and girls were abducted as the “spoils of war”. In light of the mass killing, the Yazidi Progress Party statement has now called on the government in Iraq and international organisations to intervene to facilitate the release of the remaining captives.