Other than the Peronist loyalists, what group became targets of government abductions and murder for their political dissidence?

Communists.

Explanation:

Although the 1976 military dictatorship in Argentina overthrew the Peronist government, its target and its main enemies were the communist guerrilla militants of the ERP and other socialist and communist associations. These, in their actions, allied themselves with the left factions of Peronism such as Montoneros, and began to carry out various attacks against the civilian population in Buenos Aires, Cordoba and Rosario, the main cities of Argentina. They even set up a base of operations in the interior of the country, in the province of Tucuman, where several combats between these groups and the Argentine army were carried out.

d. the right to establish a one-house legislature