BOSTON (AP) — The race to collect voter signatures ahead of next week’s deadline in the Massachusetts special Senate election is heading into a final, stormy weekend.

That could make the task even more difficult for Republican hopeful and former U.S. Attorney Michael Sullivan who is relying on an all-volunteer network to gather the needed 10,000 signatures by a Wednesday 5 p.m. deadline.

A volunteer working on the signature drive conceded Sullivan supporters are facing an uphill fight.

Democratic candidate Edward Markey’s campaign has already collected an estimated 20,000 signatures while fellow Democratic hopeful and congressman Stephen Lynch has begun the process of delivering signatures to local town and city clerks for certification.

Republicans Daniel Winslow and Gabriel Gomez are relying on a mix of volunteer and paid signature gatherers.

The election is June 25. Primaries are April 30.