Ali Motahari, who has frequently criticised the regime's indefinite house arrest of two opposition leaders, came under attack in the southern city of Shiraz last Monday, as he travelled from the airport to give a planned speech.
The 57-year-old was forced to take refuge in a nearby police station. After three hours he was escorted back to the airport and his speech was cancelled.
Motahari is a divisive political figure but the assault on him prompted 110 of Iran's 290 MPs to write an open letter of support.
Photographs have been published of some of the 50 or so protesters involved but so far there have been no arrests.
Parliament speaker Ali Larijani told MPs that the assault was "an illegal act against a member who expressed his opinion," and constituted "an action against the regime".
President Hassan Rouhani has ordered "action against the attackers", the official IRNA news agency reported on Sunday, citing the province's governor.
Motahari is one of the country's most controversial MPs.
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He has described as illegal the house arrest of Mir-Hossein Mousavi and Mehdi Karroubi, leaders of the reformist Green movement that saw millions take to the streets in protest after a disputed presidential election in 2009.
The stance puts him at odds with regime hardliners. In January, he was heckled while speaking in parliament against the house arrest of Mousavi and Karroubi.
A commotion ensued that led to the session being stopped and live state broadcasts were abruptly cut.
Mousavi, along with his wife Zahra Rahnavard, and Karroubi were placed under house arrest in 2011 after repeatedly challenging the official 2009 election results, which gave Mahmoud Ahmadinejad a second term as president.
In a letter to the head of Iran's judiciary, Motahari reportedly wrote that the house arrests were unconstitutional and that the trio should instead stand trial and be given the opportunity to defend themselves.
However, he has been accused by hardliners of provoking unrest with such comments.
Mousavi and Karroubi are accused of "sedition" against the regime and their most hardline opponents have said the two men should face the death penalty.
Ayatollah Assadollah Imani told worshippers at the main weekly prayers in Shiraz on Friday that "those who play with fire get burned."