Direct Opposites:
* Discourage: To advise against something.
* Dissuade: To persuade someone not to do something.
* Advise against: To give counsel against something.
* Deprecate: To express disapproval of something.
Less direct opposites:
* Reject: To refuse to accept something.
* Dismiss: To ignore or reject something.
* Condemn: To express strong disapproval of something.
* Criticize: To find fault with something.
* Warn: To caution against something.
* Detract: To take away from the value or importance of something.
Depending on the specific context, you might also consider:
* Ignore: To pay no attention to something.
* Overlook: To fail to notice something.
* Neglect: To fail to care for something.
The best antonym for "recommend" will depend on the specific situation and the intended meaning.