Conservatives have been accused of "panicking" over their third place in the Eastleigh by-election after a string of press reports suggested ministers were planning a clampdown on benefits for migrants.
Reports over the weekend suggested that changes could be rushed in before Bulgarian and Romanian citizens gain full rights to move to the UK at the end of the year, amid public concern about so-called "welfare tourism".
But Downing Street declined to give any timetable for the announcement of proposals and said that any changes would have to comply with European laws requiring equal treatment for UK citizens and those from other European Union (EU) states.
Labour immigration spokesman Chris Bryant said: "This Government has spent the weekend flying more kites than Mary Poppins.
"Managing immigration in a fair way is really important. Yet what we are getting from the Government is just an unseemly reaction to threats from their backbenches.
"In a panicked reaction to Eastleigh they are briefing anything and everything they can think of that they are looking at for the future, instead of properly-considered, substantive and deliverable proposals that work for everyone."
According to media reports, ministers were said to be considering making immigrants wait for up to a year after settling in the UK before being able to seek hospital care including operations, though it is understood that emergency and ante-natal treatment would be excluded from the clampdown.
The proposed changes could form part of a drive to restrict immigrants' access to benefits, council homes and public services. But it is understood that any restrictions would have to be based on residency, rather than nationality, in order to comply with EU laws - meaning that British nationals might also be required to prove their entitlement.
"We have to operate within the law, including EU single market law," Prime Minister David Cameron's official spokesman said.
"It is my understanding that one can't discriminate between EU nationalities within that law."