What is the ruling on joining secular or infidel parties (such as the Socialist Ba'ath Party) for the purpose of benefit?

It is not permissible for a Muslim to join parties founded on disbelief, such as secular, communist, socialist, or nationalist parties, even if the purpose is material gain. This is because it falls under cooperating in sin and aggression, and increasing the numbers of disbelievers. It has been narrated from the Prophet, peace and blessings be upon him, that "Among the worst people in rank with Allah on the Day of Resurrection is a servant who sacrificed his Hereafter for the worldly life of another."