First of all, Liberation Theology != Catholic Social Doctrine.
But, it is extruded by some process out of the latter of the two halves of "Catholic Economic Virtues" subsidiarity and solidarity. Whereas subsidiarity is clearly in the Bible from Jethro's advice to Moses to divide up his duties down to one person judging for just a handful of families. Solidarity is not so much in the bible, but certainly borne of it.
In the Catholic Catechism, which was compiled and published after most of this mess in the interval between Vatican II and the present, the whole of the expectations for economic activity is under the Seventh Commandment, "thou shalt not steal".
2434 A just wage is the legitimate fruit of work. To refuse or withhold it can be a grave injustice. 220 In determining fair pay both the needs and the contributions of each person must be taken into account. "Remuneration for work should guarantee man the opportunity to provide a dignified livelihood for himself and his family on the material, social, cultural and spiritual level, taking into account the role and the productivity of each, the state of the business, and the common good." Agreement between the parties is not sufficient to justify morally the amount to be received in wages.
2435 Recourse to a strike is morally legitimate when it cannot be avoided, or at least when it is necessary to obtain a proportionate benefit. It becomes morally unacceptable when accompanied by violence, or when objectives are included that are not directly linked to working conditions or are contrary to the common good. CCC 2434-2435
And specifically, with regard to the injustice between "capital" and "labor" the grave injustice mentioned above is referenced in:
"You shall not defraud or rob your neighbor. You shall not withhold overnight the wages of your day laborer. Lev 19:13
"You shall not defraud a poor and needy hired servant, whether he be one of your own countrymen or one of the aliens who live in your communities. Deut 24:14-15
Behold, the wages you withheld from the workers who harvested your fields are crying aloud, and the cries of the harvesters have reached the ears of the Lord of hosts. James 5:4
But, also the 10th commandment (and 1st beatitude) addresses and balances the disordered desire to envy the rich and gives consolation to the poor.
2547 The Lord grieves over the rich, because they find their consolation in the abundance of goods. "Let the proud seek and love earthly kingdoms, but blessed are the poor in spirit for theirs is the Kingdom of heaven." Abandonment to the providence of the Father in heaven frees us from anxiety about tomorrow. Trust in God is a preparation for the blessedness of the poor. They shall see God. CCC 2547