Smartly dressed Philipp Amthor is something of a star in Angela Merkel's conservative Christian Democratic Union (CDU). At age 27, the Bundestag MP is only half the age of the average party member. He's a frequent guest in TV talk shows and has moved up through the ranks swiftly. He joined the party in 2008 and recently became the potential top candidate for CDU chairmanship in Merkel's Baltic Sea home — which would give him a shot at becoming Germany's youngest state premier after elections next year.

Now, all of this is in jeopardy. Last week, news magazine Der Spiegel reported on Amthor's role with the US firm Augustus Intelligence (AI), founded in 2018, specializing in what it calls "secure artificial intelligence solutions."

He was on the board of directors and in 2019 he made three trips in connection with AI: to New York, Costa Rica, and St Moritz, in Switzerland. The administration of Germany's Bundestag is now investigating who paid for the trips.

The young politician also received 2,817 share options from AI, which he did not report as supplementary income. This was technically in-line with German regulations: MPs are obliged to disclose additional earnings above €10,000 ($11,000) per year — but the share options would only have to be disclosed if they had been sold for a profit.

Amthor's position with AI was also within the bounds of German law, which just requires members of Parliament to make sure that their side jobs don't take up the majority of their time.

Lobbying or corruption?

But lawmakers must not use their political mandate for private financial gain, with Der Spiegel reporting that Amthor wrote letters to the Ministry of Economics seeking "political support" for the start-up.

And that is where it gets problematic, explains Norman Loeckel of the graft watchdog group Transparency International.

"If he had been acting entirely in his role as a member of the board of directors of this company, that would be less problematic. But in this particular case, he was acting in his role as a member of Parliament, sending letters by official parliamentary mail and had meetings with the ministry in his role as a member of Parliament on behalf of that company," Loeckel told DW.

"There is a clear definition in the German law, in the criminal code: It says if a public official or a member of Parliament is taking an advantage financial or otherwise to do something in his role as public official or member of Parliament, this is corruption," he added.

Read more: How German companies donate secret money to political parties

Questions over US firm

"I'm not for sale," Amthor wrote on his Facebook profile, conceding that his lobbying had left him "politically assailable." He said he had resigned from his role on the board of directors and returned his share options.

The case also has a different dimension, as it is not quite clear what Augustus Intelligence actually does.

Some of the names on the start-up's list of supporters have raised suspicions among the German public. One of the names that pop ups most is that of Hans-Georg Maassen, Germany's former domestic intelligence chief, who left office following a discussion of his far-right leanings.

Amthor on Tuesday resigned from the Bundestag committee probing the December 2016 terror attack at a Christmas market at Berlin's Breitscheidplatz,which was set to question Maassen.

Opposition Greens co-leader Robert Habeck on Monday demanded that Amthor quit his Bundestag position as MP for Mecklenburg-Western Pomerania's coastal Greifswald area. Other German politicians have also criticized his actions, saying they damage public trust.

"The case has caused great damage to the public perception of politics in general, it has confirmed a whole series of false assumptions that MPs use their mandate for personal economic interests. It undermines public confidence in parliamentary activity," Marco Buschmann, a lawmaker with the business-friendly Free Democrats, told DW.

Showdown in Bundestag

The Amthor affair is dampening the spirits of the ruling CDU at a time when its leaders had been basking in high opinion poll results.

On Friday, the Bundestag is set to debate lobbying — this long-planned debate, which will tackle how to uncover lobbyists' activities and attempts to influence members of Parliament and ministers, now promises to be a particularly contentious one.

The Amthor case has prompted fresh demands for a mandatory German lobby register, which has met with opposition mainly from the conservative CDU/CSU bloc.

"If our coalition partner is being serious, then this week is also a moment for a political movement, structurally and not sporadically," said Katja Mast, deputy parliamentary group chairperson for the co-ruling Social Democrats (SPD).

Germany lagging in graft prevention

Transparency International spokesman Loeckel said it's hard to tell in Germany when "companies get preferential treatment" and whether their access is justified.

"For example, the car industry in Germany is a very important industry where it would be understandable if they get preferential access — rather than an artificial intelligence company from the US, where it would be hard to understand why it should get preferential treatment here in Germany," he noted.

Read more: How non-EU actors are lobbying Brussels

Debates over lobbying frequently arise in Germany, for example when high-ranking politicians take jobs in the automotive sector immediately after quitting public office.

There have been demands for top political figures to be subject to a period of restriction on leaving office, similar to the system in place in the United States.

In its latest report on corruption prevention among lawmakers, judges, and prosecutors, the Council of Europe noted that Germany had fallen short in implementing recommendations dating from 2015.

This "globally unsatisfactory" assessment has led to a "non-compliance procedure" for Germany, which means that its German delegation must provide a report on progress in implementing pending recommendations no later than 30 June 2020.

The Amthor case may well have given the issue additional momentum.