I disagree. As someone said above, talking to a lawyer does not mean filing a lawsuit. No professional business person is going to hold it against you for talking to a lawyer in a situation like this--that's what they're there for. And frankly you'd be a chump not to explore your options, but that's almost certainly what OP's founders are counting on.
I agree. The parent poster is also giving bad advice in encouraging this guy to tell his former coworkers that he does not have the money for a lawyer/lawsuit.
I'm not a lawyer, but a bit of searching online suggests that the behavior of the company may be illegal in California under a law called ERISA (see the third bullet point under "ERISA Violations" on http://www.lawyersandsettlements.com/case/stock_option.html). The onus would presumably be on the employee to establish he was fired in order to avoid having his shares vest, but if the company had no other reason to be dissatisfied with his performance and never communicated any concerns before his termination he might have a case.
Personally, I think he should ask for his full year of equity and try exchanging equity for severance if they are reluctant. The thing to remember is that he might only have been on good terms with one of the founders, which means there are group dynamics to how any action he takes will be interpreted on their side. It may also only be one of the founders who cares, and the offer may be a negotiated settlement offered from a negotiation between them rather than any specific desire to formalize anything and avoid a lawsuit.
