It is illegal for an employer to pay either sex more than the other for the same amount and type of work. Nebraska implemented the Equal Pay Act (EPA) in order to prevent pay discrimination on the basis of sex and the EPA mirrors the federal law.
The type of work done by men and women does not have to be identical, but it must be comparable for the law to apply. All employers who are covered by the Fair Labor Standards Act are subject to the EPA, which includes basically all employers.
Inform your employer about the violation. If no changes are made then you should contact the NEOC. The filing deadline for these claims in Nebraska is 4 years. However, if you want to also file a sex discrimination claim at the same time then this complaint must be filed within 300 days.