The German parliament is in session, but the chamber remains almost empty.

Where have all the politicians gone?

Their calendars are overbooked. Staying for an entire parliamentary debate takes too much time.

Lucrative side jobs are what fill up many parliamentarians' calendars.

A particularly spectacular example is Christian Democrat Reinhard Göhner, who makes at least double his salary as a parliamentarian from his work as the head of the Federal Employers Association (BDA.)

Paying for influence

Side jobs also become an issue when looking at the influence of powerful lobbying organizations in Germany. Left Party parliamentarian Gesine Lötzsch feels there needs to be more transparency.

"The interesting question is, when a parliamentarian has extra income, who ends up influencing the decision making here in the German parliament? The mandate of the Bundestag is a full-time one," Lötzsch said.

A clean image

Last year, the German parliament decided to polish its reputation by passing a law requiring more transparency. Parliamentarians were prohibited from collecting money for work they don't do, in an attempt to prevent undo outside influence. The new law also requires that parliamentarians detail their part-time work and the extra income they receive.

But nine members of the Bundestag brought a complaint before the Federal Constitutional Court in Karlsruhe, which will be heard on Wednesday.

Heinrich Kolb of the free market liberal FDP is one of the plantiffs. Kolb owns a metal business with his brother.

He worries that were he required to report his income, he would also have to disclose too much about his business, which he considers invasive.

The policy could have an unintended side effect: self-employed people and entrepreneurs might decide it's not worth leaving their civilian jobs to enter politics.

But Gesine Lötzsch insists the law's objective is to keep lobbyists from unduly influencing the political process.

"From my point of view, it's a problem when an attorney works for a large international office and then writes tax legislation. That has a dramatic effect on the federal budget. These alliances should be should be known and disclosed beforehand," Lötzsch said.