Questione giuridica chiave
Whether default interest was owed on the outstanding social security contributions after 1 January 2003.
Decisione estratta
Yes. Art. 26 ATSG does not displace the AHVV rules on when contributions become due; Art. 41bis AHVV still governs and makes interest payable on underpaid provisional contributions in this situation.
Motivazione estratta
The ATSG confirms that interest is due on matured contribution claims but does not regulate maturity itself. The AHVV implementing provisions remained applicable after 1 January 2003, and under Art. 41bis Abs. 1 lit. f AHVV the conditions for default interest were met.