TUC general secretary Frances O'Grady and trade union Unite were among those lobbying for the release of the vice-president of the Fensuagro union who was snatched by secret police at the weekend.
He had been scheduled to appear as the keynote international guest at the annual TUC Congress in a fortnight.
But it was confirmed today that he has been charged with "rebellion" and "financing terrorism" - accusations commonly levelled against trade unionists by the country's right-wing regime.
In his dual role as a labour leader and national organiser of the Patriotic March peace and social justice movement Mr Ballesteros has been at the forefront of massive strikes and demonstrations against the government's right-wing economic policies and free trade deals.
The Colombian attorney-general made what solidarity activists described as an "unusual step" of claiming publicly that the charges were unrelated to the ongoing industrial action and protests. It claimed to have uncovered incriminating evidence "on a Farc laptop" that linked Mr Ballesteros to the revolutionary group.
But British trade unionists vowed to maintain pressure on the Colombian government to secure his release.
In a letter to Colombian ambassador to Britain Mauricio Rodriguez Munera, Ms O'Grady said his detention was "deeply alarming. We are outraged to see what appears to be the old tactic of imprisoning high-profile civil society leaders by alleging involvement with terrorist groups being used again."
"Legitimate protest, including the right to take industrial action, is a fundamental part of any democracy."