Two Republican members of Congress have asked the US Treasury Department for information on what type of licence the couple obtained before heading to Havana.
The long-standing US trade embargo against Cuba prevents most Americans from travelling to the island without a licence granted by the US government.
Ileana Ros-Lehtinen and Mario Diaz-Balart, who both represent districts in south Florida where there is a high Cuban-American population, said: "Despite the clear prohibition against tourism in Cuba, numerous press reports described the couple's trip as tourism."
"The Castro regime touted it as such in its propaganda," the letter said, adding: "We represent a community of many who have been deeply and personally harmed by the Castro regime's atrocities, including former political prisoners and the families of murdered innocents."
US pop singer Beyonce and her husband, rapper Jay-Z, were mobbed by ecstatic fans on a visit to Cuba.
The pair are celebrating their fifth wedding anniversary in the capital Havana.
International superstar Beyonce has covered Camden girl Amy Winehouse's iconic Back To Black track for new film, The Great Gatsby.Read the full story ›
Beyonce hasn't given much away about her performance at half time during Sunday's Super Bowl - other than promising she'll be singing live. The singer admitted miming at Barack Obama's inauguration because she hadn't been able to rehearse properly.
She says there won't be a repeat of that in New Orleans during the game between the Baltimore Ravens and San Francisco 49ers.
As Beyonce makes final preparations, a clip has appeared online of one other thing she should avoid doing - handing the microphone to the crowd and asking them to sing along.
As a past performance proved, that can mean the song falls rather flat.
Beyonce Knowles said she mimed during her performance at Barack Obama's Inauguration Day because she is "a perfectionist."
At a NFL Super Bowl event in New Orleans the singer explained that she hadn't had a chance to rehearse with the orchestra and wanted to make the president proud.
Beyonce started the press conference with a live performance of her national anthem before asking the assembled journalists: "Any questions?"
Beyonce appears to have broken her silence over the 'lip-synching' controversy by posting a photograph of herself online wearing a jumper with the slogan: 'Can I Live?'.
The singer is thought to have 'lip-synched' the national anthem during a performance at President Obama's inauguration due to a lack of rehearsal time with the band. But up until now, she had remained tight-lipped about the incident.
The inauguration performance has prompted speculation about Beyonce's planned appearance at the Superbowl's half time show on February 3.
The top is also thought to be in reference to her husband Jay-Z's song titled 'Can I Live'.
Beyonce has announced she is reuniting with her Destiny's Child band mates for a new album - their first in eight years.
The songstress wrote on her official website, "I am so proud to announce the first original Destiny's Child music in eight years!"
The album, titled Love Songs, is due for release on 29 January.
The black-and-white album cover pictured on her website shows a sultry-looking Beyonce, Kelly Rowland and Michelle Williams.
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