The claim was public sector unions, not government employees. And the claim was 20% of votes, not 20% of workers. A substantial share of government employees are not unionized; this is particularly true of federal government employees; and a substantial share of voters are not employed (some unemployed, but more out of the workforce, looked students, homemakers, and retirees.)
And nine states leave 41, or 82% of the total, where even that far-from-what-you-originally-claimed situation still doesn't apply.