The Turnbull government would likely feel an electoral backlash in marginal seats if Sunday penalty rates are cut, polling suggests.

The long overdue decision of the Fair Work Commission on streamlining weekend pay rates is expected imminently, setting up another political brawl.

While about 60 Coalition MPs have publicly supported lowering Sunday rates and Prime Minister Malcolm Turnbull has described them as a quirk of history, Opposition Leader Bill Shorten recently shifted position from saying Labor would accept the umpire's position to proposing new rules that would ensure no worker would suffer an overall drop in pay.

Polling conducted by ReachTel for hospitality industry union United Voice in five Liberal and National Party-held marginal seats in NSW showed cutting the double time Sunday rate remains unpopular with a majority of the electorate, with twice as many people opposing any change than those who would back one.