Strictly speaking, the owners locked out the referees, so they're not striking. But to answer the main question of "why is this all happening?", the key issue is the referee pension plan. The NFL wants to switch the refs' pension plan from a defined benefit -- i.e. the league has agreed to pay a fixed benefit level regardless of where the market or economy go -- to a 401(k) type plan where they just have an account and it goes wherever the market takes it, which a) means a smaller total contribution and b) leaves all the risk to the refs. In fairness to the NFL, a lot of other companies have made this transition over time, but the refs' contention is they made life plans based around these fixed pensions. I think I read they would accept it for new refs going forward as long as the pensions for all active refs were maintained.

There are other issues:

negotiating a salary (though they're rumored to not be all that far apart on this one)

the NFL wants to add additional crews to reduce workload and create opportunties to train new refs, while the refs are worried it may leave less money to go around and lower job security if there are more crews;

the NFL wants to hire some refs as full-time employees to help train and scout future refs. The refs aren't totally opposed to the idea, but most have full-time jobs, so hashing out the details of that would take a little doing

All of the above having been said, the pension issue is the single biggest thing driving the lockout.

You said the net-net of this will cost the owners $3 million?

Versus, without it, many more bad calls and player injuries?