This email was sent out earlier from the Scott Brown Campaign:

FOR IMMEDIATE RELEASE: CONTACT: Felix Browne
January 16, 2010
MEDIA ADVISORY FOR TODAY
Dan Winslow, counsel for the Scott Brown for U.S. Senate campaign, will hold a media availability to announce the filing of a criminal complaint against the Massachusetts Democratic Party regarding a recent mailing paid for and sent by the Massachusetts Democratic Party. Winslow will make a statement and take reporters’ questions at MassGOP Headquarters in Boston TODAY at 4:00 PM.
Massachusetts GOP Headquarters
85 Merrimac Street, 4th Floor
Boston.

Scott Brown filed this complaint against the SEIU in December.
FOX News Boston reported:

BOSTON – Republican Senate hopeful Scott Brown has filed a complaint with the State Ethics Commission after a report that a union backing rival Martha Coakley used state resources to urge workers to volunteer for Coakley’s campaign.
The report by FOX25 said the Service Employees International Union used state computers and e-mail addresses to direct state employees to volunteer for Coakley, the Democratic state attorney general.
Coakley’s campaign referred questions to the attorney general’s office. A spokeswoman said the attorney general’s office has received the letter from Brown’s attorney and will review it before commenting.
The SEIU did not immediately return a call for comment.

UPDATE: Today— Brown filed a complaint against the democratic party.
The Washington Post reported:

Republican Scott Brown charged Saturday that a Democratic mailing against his U.S. Senate campaign violates a Massachusetts law prohibiting false statements against a political candidate.
The cover of a four-page mailer sent by the Massachusetts Democratic Party says, “1,736 women were raped in Massachusetts in 2008. Scott Brown wants hospitals to turn them all away.”
Brown is a state senator, and in 2005 he filed an amendment that would have allowed workers at religious hospitals or with firmly held religious beliefs to avoid giving emergency contraception to rape victims. The amendment failed, and Brown voted in favor of a bill allowing the contraception. He also voted to override a veto issued by his fellow Republican, then-Gov. Mitt Romney.