Companies both big and small can now add the plug-in alongside their own “apply now” button on corporate career sites, enabling candidates to throw their hat in the ring using their LinkedIn profile.

LinkedIn has already worked out the applicant tracking side of the equation by ensuring the candidate’s profile feeds directly into most systems. Many of the major ATS providers already began implementing the feature, and Taleo and Kenexa expect to include it within a few months.

Job boards can add the button if they so choose, but don’t count on a warm reception, especially since they get a big chunk of revenue from resume searching.

Companies pay big bucks to have access to the profiles of job seekers on job boards.  It’s safe to say that job boards won’t take kindly to LinkedIn’s latest offering, just one of many products the social site has introduced that encroaches upon job board territory.

ERE’s John Zappe points out that in the last three years especially, LinkedIn has been expanding its recruitment solutions aggressively by offering premium search tools for recruiters,  job postingsexperimenting with career toolsadding a resume-maker for candidates, and now the apply button.

LinkedIn appears to be evolving from contained professional networking ecosystem to a full-blown, 21st century job board with social sharing capabilities, something most of the job boards haven’t been able to nail down.

In fact, when Monster announced its first big foray into social media earlier this month, LinkedIn quickly stepped in to rain on their parade by cutting off access to its network. The app Monster built, called BeKnown, culled information from LinkedIn to build members’ profiles.

Monster’s indignant response to the shutdown gave us a glimpse into the increasingly hostile relationship between the job boards and the professional networking site.

But one thing is clear – LinkedIn isn’t backing off, not one bit, and today’s release is evidence of that. Whether the apply button will be widely embraced remains to be seen, but many companies, including Netflix and Photobucket, have already added the plug-in.

LinkedIn’s 100+ million membership base may be very persuasive for those who are on the fence.

Do you think LinkedIn will overtake job boards, or is this just another product they’ll move on from to create bigger and better things?

Tags: Linkedin, Kenexa, Monster, Job Listings, Taleo, Technology, Job Boards, BeKnown, Apply with LinkedIn