On its website, the Alternative for Germany, polling at around 10 percent, urged its followers to no longer buy gold, but instead donate 120 euros each, half of the sum being tax-deductible.
"If the change to party finance law is passed in a few days, as we must assume, this will create a financing gap for 2017 which will directly impact our election campaign," the party warned followers two years before national elections.
"On top of that, the retroactive application of the law poses the danger that we will have to pay back much of the money", amounting to millions of euros, it warned.
The party needs to raise two million euros by December 31, deputy party chief Beatrix von Storch told the Handelsblatt business daily, calling the new law "an existential attack on the AfD".
Under German law, parties receive state funding proportional to their vote share at the last election, plus matching contributions for what they raise in membership fees, donations and some business activities.
The AfD employed an unusual method, raising millions through an online gold shop, where it sold the precious metal at slightly above bank rates, advertising it as a safer investment than the euro currency which it wants to abolish.
So far, the matching state funds were partially calculated according to the turnover, but under the new law they will be based on the far-smaller profit margin, said the AfD in a Facebook message.
The AfD, founded in 2013 on a eurosceptic platform, has since gone through a leadership split and veered further to the right, with some of its leaders voicing support for the anti-Islamic PEGIDA protest movement.
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The party is now the chief critic of Chancellor Angela Merkel's open-door policy towards refugees as Europe's top economy faces a record influx of one million asylum seekers this year.
The AfD won 4.7 percent of the vote in 2013, narrowly missing a five-percent threshold to enter national parliament, and now hopes to send lawmakers to the legislature in 2017 elections.
Some recent polls have put it ahead of the Green Party and Left Party at more than 10 percent support, with its highest scores in the former East.
A defiant party chief Frauke Petry urged followers in a statement about the gold sales controversy to help the AfD "show the parliamentary parties that they won't defeat us in this way".