Rachel Reeves has refused to commit to scrapping the two-child benefit cap on a visit to Hamilton on Friday.
The Labour shadow Chancellor said she could not promise to get rid of the cap because the party's policies must be "fully costed and fully funded".
Reeves suggested that the limit was under consideration but that it would only be removed if there was enough money.
This comes after party leader Keir Starmer provoked outrage by saying that scrapping the cap was not Labour policy.
The policy means households with more than two children where universal credit or child tax credit is claimed no longer receive additional funds.
Reeves told reporters at British Gas’s Scottish training base in Hamilton that Labour was focused on tackling the cost of living crisis by extending the windfall tax to reduce the impact of inflation and mortgage costs.
She said: "[Shadow DWP Secretary Jonathan Ashworth] has committed to a fundamental review of how universal credit works across a whole range of areas, because this is not the only area where people have concerns about how universal credit is working.
"But you’ll know as well that I’ve said everything in our manifesto will be fully costed and fully funded. If we win the next election, we will inherit the worst economic inheritance that any government has ever been bequeathed by its predecessor.
"And that means that there are things we would like to do that we’re not able to do quite as quickly as we would want.
Reeves added that it was crucial “everything we do is built on a rock of economic and fiscal stability.”
The policy, which was brought in by David Cameron’s government, applies to additional children born after April 6, 2017, however exemptions apply for those who had children in a multiple birth or children conceived due to rape or coercion.
However, the exemptions have caused controversy as women must disclose that they were raped in order to be eligible - known as the rape clause.
The Scottish Government currently mitigates the benefit cap and devolved social security benefits are not subject to the two-child limit and rape clause.
Starmer was slammed by Scottish Labour MSP Monica Lennon after he failed to commit to scrapping the benefit cap on a visit to Kent on Thursday.
Lennon said the policy was "abhorrent" and called for party colleagues to speak out.
She also said that party members are "of deselection, being exiled to backbenches, or not winning selections" if they criticise the leadership.
Shadow DWP Secretary Jonathan Ashworth had previously called the cap "heinous" and suggested the party would scrap it.
When asked about it in Kent, Starmer said: "That isn't our policy and if it changes I'll let you know."
Scottish Labour leader Anas Sarwar Sarwar said there were no examples of candidates being deselected for their opposition to policy.
He said: “Point me to one deselection, point me to one risk of deselection or one incident in Scotland, that would suggest what has been suggested in that tweet is true.
“It’s simply not true. The only difference that I think there is, is before we didn’t have a Labour party that wanted to win. You’ve now got a Labour party that’s serious about winning and I’m never going to apologise for that.”
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