Is dropping a $60,000 dollar salary plus commission and paying someone straight commission legal?

Yes, without an employment contract, they can change your position from salaried with commission to commission-only. They can not withhold your previously earned commissions *unless* you leave the company for any reason prior to their having been paid to the company by the clients, and you had been notified of this policy in advance. They can't simply decide to make the commission-only policy retroactive.

If you have an employment agreement for the past six months for that commission, and it is being violated, you have a legitimate beef. In other words, if you are owed money for past work, the employer needs to pay you for it.

A company can do whatever they want to your pay. However, if they owe you commission from the previous 6 months, that's your money, and they don't have any right to hold it.

in most American states, the two prior posters have it correct.

the rub is in trying to collect your past commissions. It is entirely possible that your employer will decide if you do try to collect that they do not need your services at all.

whatever happens, i suggest you start looking for another job. any employer who would try to make such a policy retroactive isn't worth working for.

Probably not refuse to payed the accrual. Without a contract, the other is probably legal.

have a talk with the local Labor relations board, state or national

Yes, it happens ALL the time, to people not doing a good job.