AfD, the country's biggest opposition party after surging in 2017 polls, opposes multiculturalism, Islam and the immigration policies of Chancellor Angela Merkel, who it labels a “traitor”.
The six-year-old party was fined more than 400,000 euros in April over illegal campaign funding during regional elections.
It has also seen private donations and state funding shrink this year, AfD treasurer Klaus Fohrmann wrote in an email to party members seen by regional newspaper group RND.
“We are in serious financial distress,” he said, asking the roughly 38,000 members to come up with a further annual contribution of 120 euros.
AfD spokespeople could not immediately be reached for comment.
The April fines related to funds received by one of the party's co-chiefs, Jörg Meuthen, and another leading member, Guido Reil, from Swiss advertising agency Goal AG in 2016 and 2017, respectively.
German political parties are banned from receiving campaign funds from non-EU sources — justifying a fine around triple the original illegal contributions.
An investigation remains open into foreign donations to AfD's parliamentary leader Alice Weidel.
The party has said in the past that it has built up a one-million-euro reserve to pay for potential fines related to illegal donations.
Any new money will go into a legal defence fund the party is setting up to challenge potential close observation by Germany's VS domestic intelligence service.
Treasurer Fohrmann wrote to members Friday that a “six-figure sum” was needed to contest the possible move.
Party leaders fear that close observation by VS — tasked with fending off threats to Germany's democratic order — could count against them with voters.
AfD shook up Germany's political landscape when it won 12.6 percent of the vote in the 2017 general elections, taking dozens of seats in the Bundestag for the first time.
It scored lower in May's European election, at 11 percent.
In 2019, AfD's primary theme of migration has been largely driven out of headlines by other political topics like climate change.