WGA leaders have reminded members that they can work only for employers that have signed guild contracts — particularly in new media.

“It is the responsibility of guild members and their representatives to make sure that the company is signatory before accepting employment,” said WGA West prexy Patric Verrone and exec director David Young. “Take nothing for granted.”

The missive said that working non-union violates the WGA West’s Working Rule 8, which can lead to fines of up to the amount that the writer was paid.

WGA West spokesman Neal Sacharow said the message was sent as a result of the growing amount of work writers are doing in the realm of new media.

The WGA West reminder appears to have been primarily aimed at guild members who may be doing work for non-WGA signatory companies, e.g., Internet startups, but not taking the necessary steps of having the employer negotiate a guild contract for that work.

The message, sent Monday to 8,000 WGA West members, noted that a “major victory” of the 100-day strike was last year’s inclusion in the new contract of recognition of the WGA as “exclusive” bargaining rep for new-media writing.

“The industry hoped to make the Internet a non-union workplace and tried to get the WGA to agree that writing for new media was too ‘experimental’ to require MBA (minimum basic agreement) coverage. Fortunately, we prevailed in this struggle, and the MBA that went into effect on Feb. 13, 2008, covers the writing of audiovisual material for the Internet, mobile devices and any other technological platform considered ‘new media,’ ” Verrone and Young said in the message.

The WGA’s new-media jurisdiction is triggered by hiring either a “professional writer” (defined as a person with a screen or TV credit, 13 weeks of employment or a published novel or play that has been produced) or if anyone, even a non-WGA member, is hired to write for a project produced by a signatory company with a budget that exceeds $15,000 per minute, $300,000 per production or $500,000 per series.

“You should be proud of the gains you have won through difficult and sometimes painful struggles and sacrifices,” the duo wrote. “You should also be mindful that these hard-won gains can only be preserved by securing guild coverage in all areas of work.

WGA leaders have taken aggressive stances against those accused of violating union rules since the strike ended. They’re still in the process of holding disciplinary proceedings against Jay Leno for allegedly violating strike rules by performing his “Tonight Show” monologues while the strike was still on. And in a move that was controversial among scribes, the WGA West and WGA East last year publicly identified 28 writers — most of them working on soap operas — who resigned from the guild during the strike by filing for financial core status.