His fellow travellers say they were given no explanation about why Labor parliamentarian Khalil Eideh could not fly.
It was not until the last stop of a multi-country trip by a group of MPs that there was a problem.
It came when Khalil Eideh was stopped as he prepared to board a flight from Canada to the United States.
The group, including several other Victorian state parliamentarians and the state's assistant police commissioner, were on a taxpayer-funded study tour.
They had been examining drug laws across Europe and Canada.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
They were due to fly to the US city of Denver for their last leg when Mr Eideh was told he would not be joining them.
Sex Party M-P Fiona Patten, who witnessed the incident, says her thoughts turned to the controversial US entry restrictions on people from six mainly Muslim nations.
"I have no doubt that Khalil's mind went in that direction. He was trying to maintain composure, and he was being very composed, and he was trying to deal with this calmly and rationally."
Mr Eideh was born in Lebanon, a country not listed among those on US president Donald Trump's restricted list.
Soon after entering parliament, it was revealed he had signed a letter proclaiming loyalty to Syrian leader Bashar al-Assad, but he insisted it had been taken out of context.
Ms Patten says the delegation ensured before the trip that their documents were in order, with all members receiving special visas.
She says there is no explanation as to why Mr Eideh, who identifies as Muslim, was singled out.
"All of us travelled on official passports. Our passports were sent to Canberra not once, but twice, and we were issued with, as I say, A2 visas from the US embassy in Canberra. And that was four weeks ago. The first we heard that there was a problem was when a United Airlines staff member told Khalil that he wasn't able to board the plane."
The Victorian Government is demanding answers.
Fellow Victorian Labor parliamentarian Lily D'Ambrosio says the whole situation is deeply upsetting.
"Well, we're very concerned as a Government in Victoria that a member of parliament, a Victorian member of parliament, has been denied access to the US after having been issued with a valid visa. We've wasted no time in engaging with the Department of Foreign Affairs and Trade and US authorities to get the answers that all of us expect to be given. This is a very serious event."
Fiona Patten says she is anxious to find out the truth.
"I think this is frightening, and, frankly, I look forward to hearing why on earth they would do something like this to an Australian member of parliament."
