European Central Bank board member Juergen Stark resigned Friday, three years before his term was scheduled to end.

Stark told ECB President Jean-Claude Trichet he was leaving the board for personal reasons, but he was apparently upset over a recent bond-purchasing program, according to Bloomberg.

“Stark will stay on in his current position until a successor is appointed, which, according to the appointment procedure, will be by the end of this year, the ECB said in a statement.

Stark was appointed to the board in June 2006, but he has worked with Trichet for over 20 years. Trichet's term as president is set to end in just a few months.

The news of Stark's resignation caused an economic shock wave, pushing down European equity prices. The U.S. stock market dropped around 300 points on Friday, in part due to Stark and in part President Obama's job speech Thursday night, analysts speculate.

Germany's Deputy Finance Minister Joerg Asmussen is a likely replacement for Stark, according to a Reuters report. There are always six members of the ECB board, including the bank's president. There is also a 23-member Governing Council, which includes the six board members.