Washington (CNN) Pennsylvania's Democratic Gov. Tom Wolf has vetoed a proposed map of Republican-redrawn congressional districts, arguing the map is "a partisan gerrymander" ahead of Thursday's deadline.

Pennsylvania's Supreme Court ruled in January that the state's congressional maps must be redrawn this year. The court threw out the Republican-drawn 2011 congressional map, ruling that districts "clearly, plainly and palpably" violate the state's constitution.

"The analysis by my team shows that, like the 2011 map, the map submitted to my office by Republican leaders is still a gerrymander," Wolf said in a statement Tuesday. "Their map clearly seeks to benefit one political party, which is the essence of why the court found the current map to be unconstitutional."

A new map must be passed in the state legislature, which is controlled by Republicans, and signed into law by Wolf by Thursday, the court said. If that doesn't happen, the court said it will then draft a new map itself, using input from both parties.

The redrawing holds ramifications for the upcoming midterm elections. Republicans currently hold 12 of the state's 18 congressional districts (one is vacant pending a special election next month), but Democrats are targeting four districts this fall as they seek to flip 24 seats and retake control of the US House. New maps could shift the partisan makeup of several districts in Democrats' favor.