Amidst UK Prime Minister David Cameron’s negotiations with EU partners, he is expected to request the UK be exempt from EU laws like the agency workers’ directive, which ensures equal pay for people employed by both temporary agencies and directly by the employer. UK Unions GMB and Unite adamantly oppose the law opt-out.
See "Cameron to Include Employment Law Opt-Out in EU Membership Negotiations", Patrick Wintour, July 13, 2015