In Standard American English, a bare infinitive, i.e., one without the infinitive marker "to," is used in the objective clause after verbs such as "demand, "require," etc. So "abandon" is correct.
In formal British English, you would see "should abandon." In informal British English, you would see the indicative form of the verb used. Therefore, "abandons" is also correct.
The following is taken from The Longman Dictionary of Contemporary English:
• In everyday English, you demand that someone does something:
I demand that he apologizes.
• In formal English, you demand that someone do something, using the
base form of the verb (=the infinitive without ‘to’):
His opponents are demanding that he resign.
**✗**Don’t say: demand someone to do something
• You use the base form of the verb when talking about the past:
They demanded that he resign.
• In everyday English, people also say:
They demanded that he resigned.
• You demand that someone should do something:
His opponents demanded that he should resign.