What term refers to the legislative act that inflicts punishments on a group or person without trail?

Bill of Attainder

This is called a "bill of attainder." Both the Federal and State governments are prohibited from creating bills of attainder under Article I of the US Constitution.

Article I, Section 9, Clause 3

"No bill of attainder or ex post facto Law shall be passed."

Article I, Section 10, Clause 1

"No state shall enter into any treaty, alliance, or confederation; grant letters of marque and reprisal; coin money; emit bills of credit; make anything but gold and silver coin a tender in payment of debts; pass any bill of attainder, ex post facto law, or law impairing the obligation of contracts, or grant any title of nobility."
Bill of attainder
bill of attainder