A document banning foreign funding for political parties, had been revised twice and was adopted in the absence of the country's main Islamist movement Ennahda, which has withdrawn from the body, accusing it of being unrepresentative.
"After being postponed twice and after failed attempts to bring Ennahda back into the high authority, this bill was overwhelmingly adopted," the body's chairman, Yadh Ben Achour, told AFP.
According to independent member Zouhaier Makhlouf, 82 of the commission's 88 members approved the bill.
Ennahda is suspected of receiving funds from Gulf countries and was keen to avoid new curbs on party funding, observers say.
The law on political party funding was seen as a key step ahead of October 23 elections for a constituent assembly that would pave the way for fresh parliamentary and presidential polls.
A wave of protests by young Tunisians demanding more freedom and jobs led to the shock January ouster of Zine el Abidine Ben Ali, who had ruled the country for more than two decades with an iron fist.
The revolt tipped the first domino of the Arab spring that is still raging across the region but demonstrations have continued in Tunisia, where many have complained over the pace and depth of reform.