PORTLAND — Republican Sen. Susan Collins, who’s seeking a fourth term, has filed her nominating petitions with Maine elections officials.

Major party candidates for U.S. Senate are required to file 2,000 certified signatures by March 17. By submitting hers on Thursday, Collins beat Democrat Shenna Bellows to qualify for the ballot.

In 2008, Collins outpolled Democrat Tom Allen to win a third term, collecting more than 60 percent of the vote.

Portland lawyer Merton Henry, who’s serving as co-chairman of Collins for Senator, said the ability to collect signatures in all 16 counties was an early test of Collins’ field organization.