The confidence votes in the Senate were called by Premier Romano Prodi's government to help ensure passage of the measure in the upper chamber, where the center-left holds only a two-seat majority.
Some senators in Prodi's coalition oppose Italy's participation in the NATO mission in Afghanistan. If the government loses a confidence vote, it must resign.
The first vote, scheduled for Thursday evening, regarded the article in the decree that authorizes more than US$160 million in spending for the mission.
Overall, the measure includes US$611.4 million to continue funding 29 military and civilian missions in 18 different countries, as well as US$21.9 million for humanitarian missions in Afghanistan and in Sudan's troubled Darfur region.
The second vote, expected to take place Friday, will examine the entire bill, the Senate said.
In an interview Wednesday with The Associated Press, Prodi expressed confidence that his new government would survive the crucial votes.
The Chamber of Deputies, the lower house of parliament, approved the funding law last week by a wide margin, but the measure was supported by the conservative opposition of former Premier Silvio Berlusconi.