In 1950, B.A. Trakhtenbrot showed that the set of first-order tautologies associated to finite models is not recursively enumerable. In 1999, P. Hajek generalized this result to the first-order versions of Aukasiewicz, Godel and Product logics, w.r.t. their standard algebras. In this paper we extend the analysis to the first-order versions of axiomatic extensions of MTL. Our main result is the following. Let be a class of MTL-chains. Then the set of all first-order tautologies associated to the finite models over chains in , fTAUT, is -hard. Let TAUT be the set of propositional tautologies of . If TAUT is decidable, we have that fTAUT is in . We have similar results also if we expand the language with the Delta operator.