Labour party efforts to undermine the coalition by attacking the Liberal Democrats could backfire, Ed Balls has warned party members in an interview with politics.co.uk.
The shadow education secretary's claims are in direct opposition to David Miliband's suggestion to politics.co.uk earlier this week that Labour should seek to shorten the life of the coalition by targeting Lib Dem voters.
Mr Balls said if Labour campaigners "simply focus on fomenting discord in the Liberal Democrats" they could "take their eye off the ball" and fall into a "trap" of not presenting voters with a credible alternative.
"David Cameron would love the Liberal Democrats to fall apart. And then to say, 'you always knew these Liberal Democrats were always unreliable anyway, vote for the real thing'," he explained.
"If we haven't won the argument with David Cameron and George Osborne at that point, a Liberal Democrat collapse could not help at all."
Mr Miliband, who faces a tough fight for the Labour leadership with his brother Ed Miliband, had insisted that Lib Dem inconsistencies between their manifesto and the coalition's policies made their voters vulnerable.
Mr Balls added: I'd like to keep my focus on the economic and social strategy of Cameron and Osborne... and Labour's alternative - I think that's really where the political effort should come."
He told politics.co.uk he was uncomfortable with widespread strike action and disruption by the unions but admitted "people are going to feel very upset and hurt by what's happening".
"If Labour is simply the party of protest, if the trade unions simply fly the flag of fairness, we won't win," Mr Balls predicted.
"What we've actually got to do is be the people who say, there is an alternative, it doesn't have to be this way.
"There will be demonstrations and concerns. But you've also got to win the argument."