The three (3) main clawbacks affecting seniors are:

• Guaranteed Income Supplement
  GIS is a supplement of up to $7,608 of tax-free income paid to seniors with an income under $18,240 Individual Income and $24,096 combined income if your spouse receives the Old Age Security payment .  For every $2 of taxable income, the GIS is reduced by $1.
  
• Age Deduction Amount for seniors over 65
  If they were 65 years of age or older on December 31 of the taxation year. The maximum amount you can claim in 2018 is $7,333; in 2019, it's $7,494.  If your net income is more than $36,430, but less than $84,597, the deduction is reduced by 15%.
  
• Old Age Security (OAS) clawback
  If your 2018 net income is greater than $75,910 ($77,580 for 2019) you will have to repay 15% of the excess over this amount, to a maximum of the total amount of OAS received.
  

Cashing in RRSP's can affect all of these.  It is important that you talk to a tax professional before you cash in an RRSP.

I wrote to CARP a number of years ago about a freak law discriminating against working Seniors and to date I have not heard from CARP or any other Senior organization supporting working seniors.

Unfortunately, if a senior's only income is a government pension approximately $18,000 a year then most seniors are forced into a part time or full time job just to make ends meet.

I think that it is a little unfair but those seniors who are working MUST pay EI premiums and the company hiring them must pay the employer portion YET if the senior is laid off they are NOT ELIGIBLE to collect EI.