Colombia's government has objected to the sale of the T-shirts
A Danish fashion firm is to sell T-shirts inspired by rebel fighters, with proceeds to go to militant groups.
The T-shirts have as logos the initials of the Revolutionary Armed Forces of Colombia (Farc) or the Popular Front for the Liberation of Palestine (PFLP).
The firm, Fighters and Lovers, says it will donate 5 euros (£3) for each T-shirt it sells.
The Colombian government has protested to the Danish authorities over the sale of the T-shirts.
"Financing terrorist groups is unacceptable and goes against all the international norms," Colombian Foreign Minister Carolina Barco told private Caracol Radio on Friday.
"Yesterday our ambassador contacted the Danish government, we sent a protest note and have demanded an explanation."
The designers say Palestianian militant Leila Khaled and Colombian rebel leader Jacobo Arenas were among their inspirations.
Money from the sale of the T-shirts will help finance Farc radio stations in Colombia and a graphics studio in the Palestinian territories.
The firm's website warns that purchasers "might experience legal problems because of US or EU 'anti-terrorist' legislation, outlawing financial support to organisations labelled as 'terrorists', including the PFLP and the Farc".
The firm says Palestinian Leila Khaled was among its inspirations
Under Danish legislation introduced in 2002, anyone found guilty of directly or indirectly financing terrorist groups can be jailed for up to 10 years.
Fighters and Lovers spokesman Bobby Schultz told AFP news agency he was unconcerned.
"We are absolutely not worried about being dragged to court and sentenced. It's our customers who decide to buy our T-shirts and support these groups," he said.
"And we have the right to fight for something, for justice or the right to education, which Farc and the PLFP are fighting for."
The Farc has been involved in a 40-year conflict with Colombian state forces and right-wing paramilitary groups, in which tens of thousands of civilians have died.
It has increasingly turned to the illegal drug trade to raise funds.
The PFLP, which combines Arab nationalism with Marxist-Leninist ideology, has carried out suicide attacks inside Israel and against Jewish settlements.
It sees the destruction of Israel as integral to its struggle to remove Western influence from the Middle East.