After a bumpy week of Brexit spats within her administration and with the EU, May wants to fend off another setback in a long-awaited showdown with restive lawmakers.
MPs in the lower House of Commons will vote on a raft of amendments produced by the upper House of Lords, which May claims would weaken the government's hand in exit talks with the EU.
"We must think about the message parliament will send to the European Union this week," May told MPs in her centre-right Conservative Party late Monday.
Her minority Conservative government relies on the support of Northern Ireland's Democratic Unionist Party for a slender working majority in the 650-member Commons.
"I am trying to negotiate the best deal for Britain. I am confident I can get a deal that allows us to strike our own trade deals while having a border with the EU which is as frictionless as possible," she said.
"But if the Lords amendments are allowed to stand, that negotiating position will be undermined."