Why was the addition of new states to the union a point of contention for members of congress? they thought that their influence in congress would be diminished with the addition of new states. they were concerned that new states would become an undue financial burden on the federal government. they were concerned that the addition of a new free or slave state would tip the balance of power.

D.  They were concerned that the addition of a new free or slave state would tip the balance of power.

Explanation:

During this time, the balance between free states and slave states were crucial, if the balance between the two were tipped, that meant that they would have priority over the others. They wanted to continue to keep congressional power balanced, to avoid confrontation and negative outcomes.