Should the DUP rebel and vote with Labour, or even if they abstain, it could lead to an embarrassing defeat for the Government, which relies upon the Northern Irish party for a majority.
Labour claimed victory after even the PM's DUP allies had earlier made a decision to support their call for an end to the pay freeze for nurses, midwives, doctors and other staff. The government and Conservative MPs should stay the course, however. A Labour motion opposing tuition fee rises is also expected to be unopposed. The pay cap is hitting morale and recruitment across the health service.
Staring down the barrel of her first Commons defeat since she took the reins at Downing Street a year ago, May decided instead to avoid a damaging vote altogether.
"It's extremely rare for the Government not to vote down an Opposition motion and the only explanation is it avoided a vote because it knew it would lose it", he said.
But Health Secretary Jeremy Hunt told the Commons that Labour's motion was "bogus".
The Cabinet agreed on Tuesday to end the Tories' seven-year pay freeze, giving police and prison officers 2% and 1.7% rises respectively.
Public sector pay is now dominating the political debate - and was the main issue at the TUC conference.
Ashworth told HuffPost UK: "Theresa May and the Tories are running scared".
The vote could also tempt Tory members to oppose the Government whip, who are growing increasingly concerned about the level of debt students are graduating from university with.
"The Prime Minister is in office but not in power".
The government has been forced to back a Labour motion to give NHS workers a pay rise, after the Democratic Unionist Party signalled its support.
The DUP's 10 MPs are helping prop up the Tory Government following the snap election after entering into a confidence and supply arrangement.
Although the votes are non-binding for the government, meaning May is not obliged to act on them, it will heap pressure on the PM to make a bigger offer to public sector workers later this year.
Union leaders and Labour said the pay cap should be lifted across the sector.
It would have meant the first defeat for the Government since it took over after the General Election - highlighting Mrs May's vulnerability.