Israeli police are investigating reports that election observers from the governing Likud party were wearing hidden cameras in polling stations in Arab-majority towns.
More than 1,000 cameras were found in Arab polling stations, which the largest Arab party says were intended to intimidate Israeli-Muslims into not voting.
Likud, the party run by Israeli Prime Minister Benjamin Netanyahu, admitted equipping 1,200 election day observers with hidden cameras.
Hadash-Ta'al, an Arab political coalition, said the cameras crossed "all red lines". It called them illegal – and Israel's election authority agreed.
“The extreme right understands our strength and ability to topple the government, and is crossing all red lines, using illegal means, to interfere and prevent Arab citizens from voting,” the party said.
“But we know our strength. We’re going to vote today despite them.”
Mr Netanyahu appeared to defended the use of the cameras, saying they should be in every polling station to ensure a proper voting process, Haaretz reported.
“There should be cameras everywhere, not hidden ones,” he said.
Meanwhile, his right-wing Likud party said the problem was with the Arab community, The Times of Israel reported.
"The cameras were intended to ensure a fair vote," Likud lawyer Koby Matza said. "The problem is in the behaviour of those people in the Arab community."
But in a snap decision on Tuesday, the Central Election Committee's lawyer Hanan Melcer said filming people voting in secret was illegal.
The Likud party's lawyer claimed the cameras were not hidden "but were visible, and were placed in the community where there is a significant concern about fraud".
However, videos from the polling stations and police reports show small devices hidden in the lapels of election officials.
The Arab Balad-United Arab List party also filed an urgent complaint to the electoral committee.
"We will not surrender to the intimidation and de-legitimisation attempts," it said. "We will sit in the next Knesset and represent our public, even if Likud and the right don't want us there."
It was not the only incident against the Arab community. Hadash-Ta'al banners hanging near Nazareth were vandalised with the words "Death to the Arabs".
