Jeremy Corbyn will insist Britain "can be better off" after quitting the European Union as he says Labour is "not wedded" to freedom of movement in a major speech on Brexit.
Labour wants "fair rules and reasonably managed migration" in the settlement between the UK and EU but the country cannot afford to lose full access to the single market, the Opposition leader will say.
The speech comes after months of confusion over Labour's approach to immigration, with deputy leader Tom Watson admitting on Sunday the party's policy was unclear.
EU leaders have repeatedly warned there cannot be membership of the internal market without freedom of movement.
Opponents said the party's position on immigration was "still no clearer".
Mr Corbyn will say: "Labour is not wedded to freedom of movement for EU citizens as a point of principle.
"But nor can we afford to lose full access to the European markets on which so many British businesses and jobs depend. Changes to the way migration rules operate from the EU will be part of the negotiations.
"Labour supports fair rules and reasonably managed migration as part of the post-Brexit relationship with the EU.
"Unlike the Tories, Labour will not offer false promises on immigration targets or sow division by scapegoating migrants.
"But Labour will take action against undercutting of pay and conditions by closing down cheap labour loopholes, banning exclusive advertising of jobs abroad and strengthening workplace protections.
"That would have the effect of reducing numbers of EU migrant workers in the most deregulated sectors, regardless of the final Brexit deal."
Mr Corbyn will attack the Government over its failure to set out plans for Britain's exit.
"Not since the Second World War has Britain's ruling elite so recklessly put the country in such an exposed position without a plan," he will say.
"There can be no question of giving Theresa May's Tories a free pass in the Brexit negotiations. Unlike the Tories, Labour will insist on a Brexit that works not just for City interests, but in the interests of us all."
Criticising Brexit campaigners for ditching their pledges over the extra £350m a week that would be available for the health service after quitting the bloc, Mr Corbyn will say the "British people voted to refinance the NHS – and we will deliver it".
Labour would "take back control" over the jobs market following years of serious damage caused by "reckless" deregulation, he will say.
"Labour will ensure all workers have equal rights at work from day one - and require collective bargaining agreements in key sectors, so that workers cannot be undercut", Mr Corbyn will add.
The party would block taxpayer-funded contracts for companies head-quartered in tax havens and would not buy outsourced public services from firms "whose owners and executives are creaming off profits to stuff their pockets at the expense of the workforce and the public purse".
Mr Corbyn will say: "We will push to maintain full access to the European single market to protect living standards and jobs.
"But we will also press to repatriate powers from Brussels for the British government to develop a genuine industrial strategy essential for the economy of the future."
Liberal Democrat leader Tim Farron said Labour's immigration position was "still no clearer".
He added: "This confirms what we all suspected, that Jeremy Corbyn never had his heart in fighting to protect Britain's place in Europe.
"He failed to pull a shift to keep us in the EU before the referendum and now he is helping Theresa May, Liam Fox and Boris Johnson yank us out of the single market.
"He called for Article 50 to be invoked the day after the referendum and is now egging ministers on towards a hard Brexit."
Brexit minister David Jones said Labour would fail to take control of immigration.
He added: "Just this weekend their deputy leader admitted they don't have a policy, and Jeremy Corbyn has previously said that he's not concerned at all about numbers. They are totally out of touch with the concerns of ordinary working people."
James McGrory, co-executive director of Open Britain, said: "It is important that our country prioritises protecting the economy in the forthcoming negotiations with the EU, as Jeremy Corbyn says. We cannot allow immigration policy to dictate economic policy - we need a balanced approach that protects jobs and growth.
"Without doubt, that means full participation in the single market."