La. Stat. tit. 18 § 1294
For sixty days after promulgation of the results of an election held under this Chapter to incur debt, issue bonds, levy or increase a tax or assume debt, any person in interest may contest the legality of the election, the bond issue provided for, the tax authorized, or the assumption of indebtedness for any cause. After that time no one shall have any cause or right of action to contest the regularity, formality, or legality of the election, tax provisions, or bond authorization, for any cause whatsoever. If the validity of any election, tax, debt assumption, or bond issue authorized or provided for is not raised within the sixty days, the authority to incur or assume debt, levy the tax, or issue the bonds, the legality thereof, and the taxes and other revenues necessary to pay the same shall be conclusively presumed to be valid, and no court shall have authority to inquire into such matters.
La. R.S. § 18:1294