Usually yes. If looking sexy is part of your place of work's image, then sexy uniforms can be required. However, there should be a bona fide reason for your employer to require you to wear sexy clothing, and employers are usually not allowed to require sexy uniforms if your workplace has nothing to do with a sexy image. Some unions have successfully fought to prohibit their female members from having to wear sexy uniforms at work, but these are rare cases.
Requiring revealing or sexual uniforms where no legitimate business purpose exists may constitute sexual harassment. An employer may be liable for either sexually harassing employees or encouraging others (like fellow employees or customers) to sexually harass employees. If you feel that your employer's dress code has led to sexual harassment and violation of your labor rights, please contact your state department of labor or a private attorney.