Answer :
They believed it would weaken the Central Government. The Federalists believed in a strong Central Government, and they didn't want it to lose it's implied powers.
Answer:
The Federalists considered that the Louisiana Purchase was something unconstitutional.
Explanation:
The Federalists did not agree with the Louisiana Purchase because they thought it would affect them in terms of politics. They thought that the different states that would not be considered into the Purchase, would not be Federalist but Democratic-Republican.
They rejected the Purchase because of Constitutional grounds. They considered that the Constitution would not allow the President to do some things. For example, buying a territory. However, historians think that the real reason was related to their fear to lose political power.