Prosecutors have asked for Weidel's parliamentary immunity to be lifted, an indication that they wish to carry out a preliminary examination of the affair.
The party's other co-leader, Alexander Gauland, has so far stood by her, but the head of the party in her home state of Baden-Wuerttemberg told the Frankfurter Allgemeine newspaper she should resign if the donations turned out to have been illegal.
The party is holding a congress this weekend to choose its candidates for next year's European Parliament elections, the next major test of whether it has managed to recover the momentum that saw it burst into parliament with 13 percent of votes cast in last year's national election.
The AfD made little progress in elections in Bavaria and Hessen in October, which were both marked by surging support for the pro-immigration Greens, their ideological antithesis. ($1 = 0.8828 euros)
