You can sue them for the money: the extra 1% match was part of your compensation, and if you did the work, the employer is legally required to pay all the agreed-upon compensation. You could sue for the extra 1% they should have paid you, and if you can prove that your 401 grew during that time, possibly for the interest or capital appreciation would have received on that money. You would sue based on breach of contract--on violating the agreement (whether oral or written) pursuant to which you did work in exchange for agreed-upon compensation.