When you want to say that you approve of something or think it is the right thing to do, use the pattern “agree with something” (not “agree something”):
✗ Most Hong Kong women do not agree abortion.
✓ Most Hong Kong women do not agree with abortion.
✗ I do not agree this policy.
✓ I do not agree with this policy.
You can also use the pattern agree with doing something:
✗ As a non-smoker, I agree banning smoking in restaurants.
✓ As a non-smoker, I agree with banning smoking in restaurants.
Don’t use the pattern “agree to something” when you want to express this meaning:
✗ I agree to this opinion to some extent.
✓ I agree with this opinion to some extent.
✗ I agree to construct a second railway link to the mainland.
✓ I agree with constructing a second railway link to the mainland.
To agree to something or agree to do something means that you will do something that someone wants you to do:
Both sides agreed to some modifications in the proposals.
In the end I agreed to do the job.
Agree is not used with a direct object. Agree on/upon is used instead. In this use, it means “to decide something together” and it is mainly used when talking about official decision-making bodies and organizations.
Yesterday the management and unions agreed on a pay deal.
Leaders of Congress met to agree upon a strategy for tackling climate change.
The preposition upon is used less frequently than on, and it sounds more formal.