text: There will be posters with the slogan "liar, liar" aimed at MPs who U-turned over their pledge to oppose fee increases for universities in England.
  "We won't let them trade lies for power again," said NUS president Toni Pearce.
  "The system now is fairer than Labour's fees system," said a Lib Dem spokesman.
  The coalition government's decision to raise tuition fees in England to a maximum of Â£9,000 provoked a series of sometimes violent student protests.
  Much of the anger was aimed at the Liberal Democrats, who had targeted the student vote in 2010 with personal pledges to vote against any tuition fee increase.
  In the current election campaign, the NUS is seeking to mobilise the student vote against MPs who had promised to oppose higher fees but then voted to almost treble them.
  "I'd like to say directly to Nick Clegg that your apology won't cover any of the Â£40,000 debt that students will graduate with for the first time this summer," said NUS president, Ms Pearce.
  "They pledged to scrap tuition fees - they lied. We won't let them trade lies for power again. We represent seven million students and are urging every single one across the country to vote against broken pledges."
  This election issue includes funding for schools, university tuition fees and early years education.
  Policy guide: Where the parties stand
  The campaign will involve advertising vans, billboards and newspaper adverts, says the NUS.
  It is aimed at 28 Liberal Democrats, including leading figures such as Nick Clegg, David Laws and Vince Cable. There are also two Conservative MPs who are accused by the NUS of failing to keep a promise to oppose the fee increase.
  There were another 21 Liberal Democrat MPs who kept their pledge to vote against the fee increase.
  The NUS also published a poll of issues that will be important to student voters, which found the biggest concern is cost of living.
  There have been warnings from students of a lack of recognition for problems in paying for accommodation and living costs and lack of maintenance loans.
  Labour has promised to cut tuition fees to Â£6,000 per year, while the Conservatives want to lift the cap on undergraduate university places and have called for more value for money for students.
  Some university leaders have been critical of proposals to cut fees, arguing that higher fees have not deterred poorer students.
  University applications dipped when fees were increased, but have since recovered to record levels, with more disadvantaged students applying than when fees were lower.
  Liberal Democrat leader Nick Clegg said: "I'm not prime minister, I lead a party of 8% of MPs in the House of Commons, there was no money left... Labour had introduced and whacked up fees before we had come into office.
  "But I actually think what we did was incredibly impressive for the smaller party in the coalition, all our front page priorities we stuck to - and we will do so again."
  And a Liberal Democrat spokesman said: "There will be some people who will judge us for one thing we could not do. But many fair minded people will judge us by what we have been able to do: tax cuts for millions of working people; more money for poor children in schools; a record two million apprentices; equal marriage; shared parental leave."
target: The National Union of Students has launched a "payback time" campaign against MPs who broke their 2010 election promise over tuition fees, including leading Liberal Democrats.