Miami ( CNN ) -- For a war vet from South Florida , a leisurely road trip to a seaside vacation came to an abrupt end in Mexico , where he has languished behind bars for four months , sometimes chained to a bed . For the first few months , Jon Hammar 's parents kept his plight out of the public eye , fearing that media attention could bring harm to him in prison . But now they are coming forward , hoping the publicity will push Mexican authorities to act . Hammar , 27 , is being held in the border town of Matamoros , just across from Brownsville , Texas . It is notorious as the home of the Gulf Cartel , one of Mexico 's major drug trafficking organizations . `` The only reason they were going to stop was to get more gas , '' his father said . Hammar , who served in Iraq and Afghanistan as a Marine , was headed to Costa Rica in August to go surfing with a fellow veteran . He had surfed there before and packed every good surf board he had , his parents said . But he also took one item that quickly became troublesome : an antique shotgun handed down from his great-grandfather . Opinion : A father 's plea : End the war on drugs . He intended to hunt with it , his parents said . And he declared it with U.S. border agents . But after he drove his Winnebago a few feet farther to the Mexican side , authorities arrested him , saying the weapon did not comply with their gun laws . `` The crime that he 's charged with is possession of a weapon that 's restricted for military use , '' said his mother , Olivia Hammar . A branch of the Mexican military has said the gun is not on its `` forbidden list , '' she said . But the former Marine remains incarcerated . Mexican officials said that the files on the case were not immediately available because the arrest happened so long ago . An official at the prosecutor 's office declined to comment . A few nights after Hammar 's arrest , his parents received the first of several threatening calls from behind bars , they said . `` He said : I have your son , '' Olivia Hammar recalled , tearing up . `` I am going to f -- - him up . I already have . '' Then she heard her son 's voice . `` He said : Mom , you 've got to do what they say ; they 're really serious . '' The voice at the other end of the line asked for $ 1,800 . U.S. Sen. Bill Nelson , a Democrat from Florida , stepped in on Hammar 's behalf , speaking to Mexico 's ambassador to the United States . `` We interceded to get him out of the general prison population , '' Nelson said . This served to remove Hammar from contact with dangerous inmates . The calls have since stopped , his mother said . `` He is now being kept in a low ... intensity place , more like an administrative place , '' Nelson said . But because of the low security of the new facility , which Olivia Hammar describes as a storage shed , officials periodically chain Hammar to his bed . The Hammars recently turned to their U.S. congresswoman , Ileana Ros-Lehtinen , who heads the Committee on Foreign Affairs . `` This is outrageous , '' Ros-Lehtinen said . She has spoken with the State Department and the U.S. ambassador to Mexico , and will meet with the Mexican ambassador to the United States this week . `` Enough is enough , '' she said . `` Jonny , we 're going to get you out of there , '' Olivia Hammar said to her son by phone Friday . He reminded her that she has been telling him that since August . Their son returned to them safe and unharmed from Iraq and Afghanistan . Hammar 's parents now fear they could lose him just across the border , if they wait too much longer . Mexico says Gulf Cartel boss arrested . CNN 's Gary Tuchman reported from Miami and Ben Brumfield wrote from Atlanta .
Jon Hammar is being held in a town dominated by a drug cartel . The show has been criticized for its portrayal of the Mexican cartels, which are often portrayed as ruthless and brutal. He served in Iraq and Afghanistan .