Victorian Labor MP Khalil Eideh still doesn't know why he was barred from entering the United States, but his premier says he handled the "confronting" treatment with class.
The upper-house MP was on a study tour with fellow politicians in Vancouver when he was rejected from a flight to Denver on Friday, despite having a valid visa organised through the Australian government.
"I've been discriminated against," Mr Eideh told reporters when he returned to Melbourne on Saturday.
"I'm very, very disappointed and frustrated."
Premier Daniel Andrews says he has not been told why Mr Eideh was barred from the US, despite the government seeking answers from authorities.
"He's a person of integrity, a good friend, someone who I can't understand why he would be denied entry into the United States; that's really a matter for them to explain," Mr Andrews told reporters on Monday.
"It would have been a very confronting thing to have to deal with, but he's handled it very well, I think he's handled it with some class."
Mr Andrews says the former trucking magnate did not deserve the treatment.
Mr Eideh, born in Lebanon to Syrian parents, had a visa for his US travels, and he said American authorities had not raised any issues during the application process.
The US Embassy referred questions on the ban to US Customs and Border Protection, which has not responded to questions.
Mr Eideh signed a letter in 2002 professing loyalty to Syrian dictator Bashar Al-Assad while seeking to get the Syrian Honorary Counsel in Melbourne removed.
But when the letter was made public in 2006, Mr Eideh said he had only added his signature to the letter which was penned by someone else, and he was loyal to Australia.
Mr Eideh has family in Syria and last visited the country over the Christmas break.
He doesn't believe US President Donald Trump's travel ban, which denies entry to America by citizens of Sudan, Somalia, Iran, Yemen, Syria and Libya from travelling to the US, is behind his refused entry.
A spokeswoman for Foreign Minister Julie Bishop on Friday said Australian officials are making urgent enquiries about what had happened, but have released no further information.
