Colombia's government announced on Monday that undocumented Venezuelan migrants would be excluded from its mass vaccination program against the Covid-19 virus.
That amounts to around 55 percent of the 1.7 million Venezuelans living in Colombia.
"Those who don't have Colombian nationality and whose migration situation has not been regularized, of course they won't" be vaccinated, President Ivan Duque told Blu Radio.
He said the measure was necessary to avoid "a call to stampede, where everyone crosses the border to be vaccinated."
Five million Venezuelans have left their country since 2015, according to the United Nations.
They have fled Venezuela's economic meltdown that has resulted in the world's highest inflation and seven years of recession.
Neighboring Colombia is home to the single largest contingent of Venezuelan migrants.
The government says it will begin a mass immunization program in February and has secured 40 million doses for its 50 million population.
Duque has said he will prioritize Colombians but added that documented Venezuelans would be subjected to the same criteria in deciding who receives the vaccine first.
The president has come under fire for his statements, though.
"From an epidemiological point of view it's a bad idea to not vaccinate Venezuelans," former health minister Alejandro Gaviria wrote on Twitter.
"But most of all it's an unethical proposal. It excludes the most vulnerable and discriminates in an almost menacing way a group of people based on their nationality and migratory status."
Colombia has been one of the worst hit countries in Latin America by the pandemic with more than 1.5 million cases and over 40,000 deaths.