Andrew Mitchell should be sacked by the Prime Minister, Yvette Cooper said as Labour stepped up its attacks on the embattled chief whip.
The shadow home secretary said the time had passed for clarifications and apologies over Mr Mitchell's alleged use of the word "pleb", and said David Cameron had to act.
Labour has previously raised questions over Mr Mitchell's ability to stay in his post, which he gained in last month's reshuffle, but has stopped short of calling for his resignation or for Mr Cameron to sack him.
Mr Mitchell, who was accused in news reports of a foul-mouthed rant at Downing Street police officers when they would not let him cycle through the street's main gate, has apologised for not treating officers with respect but denied calling them plebs.
Ms Cooper's call comes ahead of a meeting between Mr Mitchell and the West Mercia Police Federation in his Sutton Coldfield constituency.
She said: "This has gone on long enough. Neither the Prime Minister nor the chief whip have proved capable of coming clean swiftly and putting this right. And it is now clear no one even in the Conservative Party has confidence in Andrew Mitchell either.
"The failure by David Cameron and Andrew Mitchell to take this incident seriously enough and to sort it out straight away means Andrew Mitchell will clearly not be able to instil respect in Parliament or beyond as chief whip, and this will just drag on and on. David Cameron needs to put an end to this now and remove Andrew Mitchell from his position as chief whip."
Mr Mitchell has faced repeated calls for clarification about the incident.
Mr Cameron has insisted that what happened was wrong and should not happen again but has not gone further, highlighting that the officers involved wanted to draw a line under the affair.
Mr Mitchell did not attend this week's Conservative Party conference amid speculation that he could yet lose his job, weeks after the initial report in The Sun.