Claudia Julieta Duque (pictured) was due to travel to the UK next week as a guest of the NUJ. She was made an honorary member of the union earlier this year.
NUJ general secretary Jeremy Dear said: "Claudia is in Europe to receive awards for her brave and courageous work documenting human rights abuses in Colombia. It is shameful that the UK government is the only one to turn down her visa request for what appear to be political reasons. The decision should be reversed as a matter of urgency".
IFJ general secretary Aidan White said: "At a time when the international community should be cracking down hard on impunity and the violations of journalists' rights, it is extraordinary that the authorities in Britain are closing the door to one of Colombia's most distinguished reporters who work is an inspiration in the struggle for democracy and human rights."