A cross-party group of pro-EU MPs are making a concerted push to get the UK government to drop its controversial and "unachievable" immigration pledge.
Conservative Anna Soubry, Labour's Pat McFadden, and Liberal Democrat Norman Lamb wrote to ministers on Tuesday (4 March) about the "tens of thousands" net migration target.
The Open Britain supporters warned that the UK could be denied skills, talent and labour if the Conservative general election manifesto pledge is met.
"In today's world, immigration is a fact of life. Thousands of people from inside and outside the EU make a positive contribution to the UK, just as thousands of British people do all over the world," the MPs wrote.
"Moving abroad is not a crime and not a threat. It's the way the world works and most people who do it are determined to do a good job wherever they go.
"EU migrants make a vital contribution to our country. They bring innovation and ideas to our economy; they pay taxes that help us invest in our public services; and they are our friends, family and neighbours.
"This is why we are concerned about the economic and social implications of plans to dramatically reduce migration to the tens of thousands."
This campaign is backed by the Migration Matters Trust, the Royal College of Midwives and HR body the Chartered Institute of Personnel and Development (CIPD).
"The idea that there is an optimal level of net migration is a total myth. Fluctuations in labour demand, caused by sectoral or seasonal changes, or the economic cycle, mean that we need a labour market that can flex to the demands of the economy," said Ben Willmott, head of public policy at the CIPD.
"Instead of worrying about setting an arbitrary target for net migration the focus for policy makers should be on designing a flexible immigration system that provides the labour and skills the UK economy will need to grow and compete in the future post-Brexit."
The latest data from the Office for National Statistics (ONS) estimated that net migration will hit more than 273,000 in the year to September 2016, down 49,000 on the year before but still almost triple the "tens of thousands" target.
The issue became a hot topic during the EU referendum, with the Vote Leave campaign endorsing an Australian-style points system. But Brexit Secretary David Davis recently told a BBC One Question Time audience that immigration numbers may go up after the UK splits from the EU in 2019.
"I cannot imagine that the policy will be anything other than that which is in the national interest, which means that from time to time we'll need more, from time to time we'll need less migrants," he said.
The Home Office had not responded to a request for comment at the time of publication.