The colloquial British-English expression Irishman’s rise denotes a fall in value, especially a reduction in wages.

The following, for example, is from Mersey Mastermind, a quiz published in the Liverpool Echo (Liverpool, Merseyside, England) of Saturday 27^th December 1997:

What is an Irishman’s rise?
[Answer:] A pay reduction.

Irishman’s rise is one of several expressions denoting the opposite in meaning of the noun qualified by the genitive case of Irishman. Among such expressions are:
– Irishman’s promotion, denoting a demotion;
– Irishman’s hurricane, denoting, in nautical slang, a flat calm.

To Irishman’s hurricane, Irishman’s promotion and Irishman’s rise correspond the expressions Irish hurricane, Irish promotion and Irish rise. The earliest occurrence of Irish rise that I have found is from the Kentish Mercury, Greenwich, Woolwich, and Deptford Gazette (Greenwich, Kent, England) of Saturday 10^th June 1848:

An Irish Rise.—A valiant dockyard volunteer employed in the Dockyard, applied to the Board of Admiralty, for a rise in his weekly wages, which were £1 2s. 6d. as they were not sufficient for his “rank.” The Board ordered an investigation to be made into his “meritorious services” which proved so good that they promised him a “rise” to drill serjeant’s “rank and pay” of 16s. 6d. per week, which to the horror and astonishment of the applicant, mulcted him of 6s. per week in his pay, he now wishes to recall it, but it is too late: so he gains nothing by his avaricious motion.

A variant of Irishman’s rise and Irish rise is Paddy’s rise.

Paddy, pet form of the Irish given name Padraig, denotes an Irishman—cf. the Scouse expression Paddy’s Wigwam.

The earliest occurrence of Paddy’s rise that I have found is from a letter to the Editor, by a person signing themself ‘A Suffering Ratepayer’, published in The Shields Daily News (Shields, Northumberland, England) of Wednesday 14^th May 1879:

Sir,—I was pleased to see a letter in the “Shields Daily News” of Saturday signed W.W.A., animadverting on Mr Younger’s request for an increase of salary. I heartily endorse the sentiments conveyed in that letter. Instead of giving public officers an increase at the present moment, I feel convinced they ought to get (“Paddy’s rise”) a general reduction all round. […] Every public servant ought to have at least 25 per cent taken off his salary just now, and when better times come, and the Ratepayers can afford it, the salaries can be restored to their old figure.

The earliest occurrences of the expression Irishman’s rise that I have found are as follows, in chronological order:

1-: From the following letter, published in Lloyd’s Weekly London Newspaper (London, England) of Sunday 16^th May 1847:

Boroughbridge Letter Carrier.—“Sir,—Knowing you to be an advocate for the rights of man, and woman too, I take the liberty of asking your counsel and advice respecting a public servant, who, I think, must have been forgotten, when the salaries of some less worthy personages were fixed, or she must, in justice, now be fully entitled to large compensation for having been so long neglected. The letter carrier for Boroughbridge (an ancient town, which did return two members to Parliament), is a woman. She assists daily, in the post-office, in sorting the letters and papers for Boroughbridge, and then delivers them; and for performing this on seven days per week, she receives annually £2 10s., without prospect of any increase, except in the number of letters; and she will have, when the railway is opened next month, to deliver twice, instead of once, daily! The poor woman is afraid of asking for an advance, fearing that they may give her the ‘Irishman’s rise,’ from her 1½d. per day to nothing, giving her situation and salary to another. She must surely think that the Duke of Newcastle holds her appointment, the same as he once did Boroughbridge and Albro’, as freehold, and that he still claims the right of doing as he likes with (her) his own.—“A Lover of Justice to All.”

2-: From The Provinces, published in Lloyd’s Weekly London Newspaper (London, England) of Sunday 18^th November 1855:

Hampshire.—The Shipwrights’ Strike at Southampton.—Since our last publication many of the men, finding that there was no likelihood of their being enabled to induce the masters to agree to the rise in their wages of 1s. per day, have returned to their work at 5s. per day as formerly, the high price of provisions and the want of funds rendering it impossible for them to hold out for any longer period. It is said that some are even so anxious to procure employment that they are willing to accept what is termed an “Irishman’s rise,” viz., to work for sixpence a day less than heretofore. When a strike took place among the shipwrights five or six years since, it was then attended with a similar result, the trade generally agreeing to accept sixpence per day less wages rather than remain for any length of time out of employment.—Hampshire Independent.

3-: From a letter to the Editor, by a person signing themself ‘A Ratepayer’, published in The Burnley Advertiser (Burnley, Lancashire, England) of Saturday 2^nd April 1859—a shilling was equal to twelve pence:

Sir,—Whilst perusing your paper of Saturday last, I was somewhat surprised to find that the Assistant Overseer had made application for another advance of salary, and should like to warn him, that if he is not very careful he will stand a very good chance of losing his shop […]. I can well remember being at the meeting in 1855, when he and others were candidates for the office; and he then valued his services at £70 a year, and agreed to devote the whole of his time to the service of the rate payers; so that whatever he may have said in answer to the chairman, or whatever may have been the amount of his first years’ drawing, his agreement was for £70. Since then he has been raised to £100; and I am of opinion that no valid reason has been assigned why that advance has taken place. […] We engaged Mr. Parkinson at his own valuation, £70 per annum. He has been raised stealthily, and if not content, let him give fair warning to the ratepayers generally, and I am of opinion that he will get the Irishman’s rise from two shillings to eighteenpence!