Chancellor Angela Merkel's conservatives sought on Wednesday to end corruption allegations roiling their ranks over mask procurement, ordering MPs to declare all financial gains related to the pandemic days ahead of key regional elections.

A lawmaker from Merkel's CDU Party and another from its CSU Bavarian sister party have been accused of profiting directly or indirectly from mask contracts.

In a move to clean house, the conservative CDU-CSU alliance on Wednesday ordered all of its MPs to declare any financial benefits gained from the coronavirus pandemic by 6pm on Friday.

All members of the CDU-CSU parliamentary group will have to make "a declaration that no such benefits were obtained in the context of the COVID-19 pandemic", says the letter addressed to the lawmakers, dated March 10.

This declaration must take into account any financial benefits "from the purchase or sale of medical products such as protective equipment, testing and vaccination supplies, from the provision of contacts, from the forwarding of offers or enquiries, or from the provision of support or advice to third parties", the letter seen by AFP says.

In the event that such a declaration cannot be made, MPs are urged to report directly to two senior party members.

CSU lawmaker Georg Nuesslein was last month placed under investigation for corruption following accusations that he accepted around 600,000 euros ($715,000) to lobby for a mask supplier.

A similar controversy has embroiled CDU lawmaker Nikolas Loebel, whose company pocketed 250,000 euros in commissions for acting as an intermediary in mask contracts.

Loebel has resigned from his MP post and Nuesslein has said he will leave after September's elections, with the deals drawing scathing criticism across the political spectrum.

Amid the fallout from the scandal dubbed the "mask affair" by German media, the conservatives said they had "a responsibility to present and clarify such matters in a completely transparent manner".

The scandal has led to a drop in the CDU's popularity ratings just days ahead of two key regional elections in Baden-Wuerttemberg and Rhineland-Palatinate.

The state elections will be a litmus test ahead of Germany's general election on September 26 — the first in over 15 years not to feature outgoing chancellor Merkel.