Two US Republican lawmakers want to know if popular American pop star Beyonce and her husband, rap singer Jay-Z, had the US government's permission to travel to Cuba despite an economic embargo.

Representatives Ileana Ros-Lehtinen and Mario Diaz-Balart of Florida on Friday sent a letter to Adam Szubin, director of the Office of Foreign Assets Control at the US Treasury Department, requesting information on the type of license Beyonce and Jay-Z received before traveling to Cuba.

"As you know, US law expressly prohibits the licensing of financial transactions for 'tourist activities' in Cuba," the pair wrote.

The lawmakers went on to say that these restrictions were in place because the Cuban government was listed by the US State Department as one of four state sponsors of terrorism and has "one of the world's most egregious" human rights records.

"Cuba's tourism industry is wholly state-controlled; therefore, US dollars spent on Cuban tourism directly fund the machinery of oppression that brutally represses the Cuban people," Ros-Lehtinen and Diaz-Balart wrote.

Beyonce and Jay-Z created a stir Thursday as they toured the streets of Old Havana, with hundreds of Cubans turning out to catch a glimpse of the US pop power couple.

Celebrating their fifth wedding anniversary, they visited historical landmarks in the heart of Old Havana, which is a UNESCO World Heritage site. They snapped pictures and spoke with local residents.

Beyonce -- who sang the US national anthem at President Barack Obama's inauguration in January and performed in the Super Bowl half-time show in February -- was wearing a short mustard yellow dress with black and white accents.

After visiting the cathedral, the couple had lunch in a nearby restaurant.

On Wednesday night, they also had dinner at La Guarida, one of Havana's most exclusive restaurants.

Americans are not allowed to visit Cuba and spend money there unless they have special US government permission.

According to regulations posted on the Treasury Department's website, "unless authorized by a general or specific license, any person subject to US jurisdiction who engages in any Cuba travel-related transaction violates the regulations and may be subject to penalties."

Criminal penalties for violating the regulations could result in up to 10 years in prison and $250,000 in individual fines.

Thousands of Americans nevertheless visit Cuba every year without US permission, often via third countries. They are rarely prosecuted back home unless they flaunt their defiance of the rules.

Beyonce is a strong and vocal supporter of Obama and helped raise money for his 2012 re-election campaign.

In their letter, the Republican lawmakers noted that numerous press reports described the couple's trip as tourism and that the Cuban government had touted it as such in its propaganda.

"The restrictions on tourism travel are common-sense measures meant to prevent US dollars from supporting a murderous regime that opposes US security interests at every turn and which ruthlessly suppresses the most basic liberties of speech, assembly, and belief," argued Ros-Lehtinen and Diaz-Balart, both Cuban-Americans. "We support the Cuban people by refusing to sustain their jailers."

Beyonce and Jay-Z were not the only US celebrities to visit Cuba in recent years -- actors Sean Penn and Bill Murray did so in 2009.