What did the union fear would happen when Texas requested annexation?

1. That it might into war with Mexico.

2. Fear of power shifting to the south.

3. Fear of return of slave trade.

Explanation:

Texas Annexation of Texas into the United state of American was a result of the convention of 1845 which was aimed at admitting Texas into the union. This convention of admission made Texas the 28th state to be admitted into the union.

However, the union over Texas annexation feared that the power in the congress will shift move to the south more than the north. The union was not comfortable with the annexation because it might result in a war with Mexico. After all, Mexico still wanna hold on to Texas. The union also believe that as Texas is a slave trade known state, the business of the slave trade might return.