Rep. Rashida Tlaib, Michigan Democrat, was called out Monday after Palestinian activist Abbas Hamideh, a staunch defender of the terrorist group Hezbollah, posted photos of the two of them posing at her swearing-in ceremony in Detroit.

Mr. Hamideh tweeted a photo of himself Saturday with Ms. Tlaib along with the caption, “I was honored to be at Congresswoman @RashidaTlaib swearing in ceremony in #Detroit and private dinner afterward with the entire family, friends and activists across the country.”

Critics were quick to point out that Mr. Hamideh, a co-founder of the pro-Palestinian group Al-Awda, which means “right of return,” has a history of praising Hezbollah leaders such as Sayyed Hassan Nasrallah and declaring that Israel has no right to exist.

In December 2015, Mr. Hamideh called convicted terrorist Samir Kuntar a “legendary Hezbollah martyr,” days after he was killed in an explosion in Damascus. Kuntar was convicted of murder and terrorism for his role in a 1979 attempted kidnapping that resulted in the deaths of four Israelis but was released in a 2008 Israeli-Hezbollah prisoner exchange.

Max Samarov, executive director for research and campus strategy of the pro-Israel group Stand With Us, said that Mr. Hamideh has a “long record” of incendiary rhetoric.

“Just one example: He called Hezbollah leader Hassan Nasrallah ‘the most honorable man on earth,’” Mr. Samarov said, referring to a February 2016 social media post. “Hassan Nasrallah has made genocidal threats against Jews, he has actively aided the dictator Bashar al-Assad in the mass murder of the Syrian people.”

Mr. Samarov said he was unaware of any other member of Congress meeting with Mr. Hamideh. Ms. Tlaib’s office did not return immediately Monday a request for comment.

“So there’s a litany of disturbing comments along these lines,” Mr. Samarov said. “No member of Congress, Republican or Democrat, should be associating with people who are racist or who support violence against innocent people.”

He said Al-Awda has “expressed a lot of really extremist views. I see them as a hate group.”

Mr. Hamideh responded to social-media criticism Monday by doubling down on his past blasts at Israel, tweeting, “The illegal terrorist entity of ‘israel’ doesn’t have a right to exist on top of stolen Palestinian land.”

“Criminal Zionists are going apes—t over one picture. Imagine when we take selfies in a liberated Jerusalem?” Mr. Hamidehtweeted.