Victorian State MP Khalil Eideh has been blocked from entering the United States while on an overseas study tour.

The Upper House MP, who was born in Lebanon, was part of a group of MPs examining the effectiveness of drug laws and regulations in Europe and North America.

But when he went to fly from Vancouver to Denver he was told his flight had been cancelled by the US.

Mr Khalil and other MPs had official visas to travel, so it is not clear why he was not allowed into the country.

The Muslim MP is still in Canada but is returning to Australia soon.

His Labor colleague Natalie Suleyman, who is also Muslim, said it was a distressing experience.

"It was upsetting to see your colleague go through this,'' Ms Suleyman told the ABC from Denver.

"It was a really shocking experience."

While born in Lebanon, Mr Eideh has been linked to Syria over a letter he wrote to president Bashar al-Assad in 2002, which he later said was taken out of context.

A spokesperson for Foreign Minister Julie Bishop said the minister had asked Australian officials to make urgent enquiries.

"Like Australia, the United States administers a strict entry regime and the decision on who can enter the country is a matter solely for the US Government," the spokesperson said.

"Australian consular officials stand ready to provide assistance, should it be required."

Eideh travelled to Syria with other MPs

A parliamentary travel report showed Mr Eideh travelled with three other state MPs to Syria in 2007.

The MPs visited Syria and Dubai to "look at trade issues in the fast-growing country Qatar" and also to "witness the refugee crisis that had been created in the Middle East by the invasion of Iraq."

Mr Eideh and the delegation met with the vice-president of al-Assad's Baathist Party, Najah Al-Attah.

The delegation also visited the Syrian Parliament and met with the speaker and ministers, and several governors.

President Donald Trump has moved to have people from Syria banned from entering the US.

Sex Party Upper House MP Fiona Patten, who was travelling with Mr Eideh, said she could not understand why he was singled out.

"I do look forward to hearing why this occurred to our colleague when he had travelled in numerous other countries, when he had been given the same visa that all of us had been given," she said.

'Serious questions have to be answered'

Victorian Government Minister Lily D'Ambrosio said Mr Eideh's Labor colleagues were concerned about his "unfair" treatment.

"There are serious questions that have to be answered," she said.

"To actually prevent a Member of Parliament to enter the US is something that really does raise some very serious concerns about the internal operations of the US system."

US Customs and Border Protection branch chief Jaime Ruiz said only a small number of the more than 1.2 million people who entered the US each day were denied entry.

"It is important to travellers to know that having a valid visa does not guarantee entry to the United States," he said.

"A visa allows a traveller to knock at the door — travel to a port of entry, airport or land border crossing and request permission to US Customs and Border Protection.

"All travellers must clear admissibility laws."

The US Consular General in Melbourne said it was unable to comment on individual cases for privacy reasons.

The Victorian Government had asked the Department of Foreign Affairs and Trade (DFAT) for an explanation from the US authorities about why Mr Eideh was refused entry, a spokesman said.

Mr Eideh is the deputy president of the Legislative Council and has been an MP since 2006.