BERLIN, March 21 (Reuters) - An influential figure in Bavaria's Christian Social Union resigned all party offices on Sunday, a newspaper reported, the latest politician caught up in a scandal over kickbacks in face mask procurements that has cost Chancellor Angela Merkel's conservative bloc in opinion polls.

Alfred Sauter, a member of the wealthy southeastern state's parliament, is being investigated by prosecutors over allegations he took bribes in return for helping arrange public mask procurement contracts during the coronavirus pandemic. He denies the allegations.

Sauter, whose decision to stand down was reported in the Augsburger Allgemeine newspaper, is at least the third conservative politician to have resigned in the scandal over mask procurement kickbacks.

A member of the CSU's board, Sauter has been a mover-and-shaker in the party for a quarter of a century, serving for a period as Bavaria's justice minister. As of Sunday, he was still listed as a member of the Bavarian parliament and it was not clear if he also intended to step down from parliament.

With a national election due in September, at which voters will choose a replacement for Merkel, who is not running for a historic fifth term, the affair comes at the worst possible time for the conservative bloc.

A Kantar poll on Sunday showed support for the Christian Democratic Union-CSU ticket at 27%, just five points ahead of the Greens. In May, when Merkel was winning plaudits for her management of the pandemic, support stood at 40%.

Bavarian premier Markus Soeder, who is a leading candidate to run as conservative candidate to replace Merkel, is due to hold a news conference on the affair at 1200 GMT. (Reporting by Thomas Escritt)